Ratio metric position sensor and control system

ABSTRACT

The subject matter of this specification can be embodied in, among other things, a position sensor system that includes a sensor housing defining a first cavity having a first face, a fluid effector including an actuator housing having an inner surface defining a second cavity, and a moveable body having a second face and configured for reciprocal movement within the second cavity, an acoustic transmitter system configured to emit a first emitted acoustic waveform toward the first face, and emit a second emitted acoustic waveform toward the second face, and an acoustic receiver system configured to detect a first reflected acoustic waveform based on a first reflection of the first emitted acoustic waveform based on the first face, and detect a second reflected acoustic waveform based on a second reflection of the second emitted acoustic waveform based on the second face.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a continuation-in-part of and claims the benefit ofpriority to U.S. patent application Ser. No. 16/987,828, filed Aug. 7,2020, the contents of which are incorporated by reference herein.

TECHNICAL FIELD

This instant specification relates to ultrasonic position sensors.

BACKGROUND

Position measurement devices are used for the characterization andoperation of fluid control systems. Traditionally, effector (e.g., valvebody, piston head) position tracking is achieved through the use oflinear variable differential transformers (LVDTs). LVDTs drive systemsizing and introduce accuracy and sizing constraints. Specifically,actuation devices generally require the LVDT be installed through thepiston rod, driving actuator sizing.

Ultrasonic position sensors are a proven industrial technology that canbe leveraged for position detection. Existing time of flight ultrasonicposition sensors emit acoustic pings and measure the amount of timeuntil reflected echoes of the pings return. The amount of time betweenthe transmission and return of the pings is generally dependent upon thedistance between the transceiver and the object being measured, and thespeed of sound in the medium through which the pings are beingtransmitted. That speed of sound is dependent upon the characteristicsof the medium, such as its density, temperature, and/or acousticimpedance. Existing time of flight ultrasonic position sensors dependupon on predetermined knowledge or determination of the speed of soundthrough the medium through which the pings are being transmitted inorder to function. In applications such as fuel valves and pressureregulators, the temperatures and types of fuels used can vary, which cancause the speed of sound to vary dynamically during operation. The speedof sound of a medium can be sensed, but the inclusion of theseadditional sensors adds to the complexity, size, cost, and weight ofsuch systems.

SUMMARY

In general, this document describes ultrasonic position sensors.

In an example embodiment, a position sensor system includes a sensorhousing defining a first cavity having a first face, a fluid effectorincluding an actuator housing having an inner surface defining a secondcavity, and a moveable body having a second face and configured forreciprocal movement within the second cavity, an acoustic transmittersystem configured to emit a first emitted acoustic waveform toward thefirst face, and emit a second emitted acoustic waveform toward thesecond face, and an acoustic receiver system configured to detect afirst reflected acoustic waveform based on a first reflection of thefirst emitted acoustic waveform based on the first face, and detect asecond reflected acoustic waveform based on a second reflection of thesecond emitted acoustic waveform based on the second face.

Various embodiments can include some, all, or none of the followingfeatures. The position sensor system can include a timer configured todetermine a first time of flight of the first emitted acoustic waveformand the first reflected acoustic waveform, and determine a second timeof flight of the second emitted acoustic waveform and the secondreflected acoustic waveform. The position sensor system can include aprocessor system configured to determine a position of the moveable bodywithin the second cavity based on the first time of flight and thesecond time of flight. The acoustic transmitter system can be configuredto emit one or both of the first emitted acoustic waveform and thesecond emitted acoustic waveform through a fluid in one or both of thefirst cavity and the second cavity, and the acoustic receiver system canbe configured to receive one or both of the first reflected acousticwaveform and the second reflected acoustic waveform from the fluid inone or both of the first cavity and the second cavity. The acoustictransmitter system can be configured to transmit the second emittedacoustic waveform at a predetermined emitted frequency, and the acousticreceiver system can be configured to determine a reflected frequency ofthe second reflected acoustic waveform. The position sensor system caninclude a processor system configured to determine a speed of themoveable body based on the predetermined emitted frequency and thereflected frequency. The fluid effector can be a linear piston effector,the first cavity can be a first tubular cavity having a firstlongitudinal end and a second longitudinal end defining the first faceopposite the first longitudinal end, the second cavity can be a secondtubular cavity having a third longitudinal end and a fourth longitudinalend opposite the third longitudinal end, the moveable body can be apiston head configured for longitudinal movement within the secondtubular cavity, the acoustic transmitter system can include a firstacoustic transmitter arranged at the first longitudinal end and a secondacoustic transmitter arranged at the third longitudinal end, and theacoustic receiver system can include a first acoustic receiver arrangedat the first longitudinal end and a second acoustic receiver arranged atthe third longitudinal end. The position sensor system can include aunified cavity having the first cavity and the second cavity. The firstface can be at least partly defined by a shoulder extending betweenfirst cavity and the second cavity. The acoustic transmitter system caninclude a first acoustic emitter configured to emit the first emittedacoustic waveform toward the first face, and a second acoustic emitterconfigured to emit the second emitted acoustic waveform toward thesecond face. The second acoustic emitter at least partly concentricallysurrounds the first acoustic emitter. The position sensor system caninclude a phase detector configured to determine a difference between atleast one of (1) a first emitted phase of the first emitted acousticwaveform and a first reflected phase of the first reflected acousticwaveform, and (2) a second emitted phase of the second emitted acousticwaveform and a second reflected phase of the second reflected acousticwaveform. The position sensor system can include another moveable bodyhaving a third face and configured for reciprocal movement within athird cavity, wherein the acoustic transmitter system is configured toemit a third emitted acoustic waveform toward the third face, and theacoustic receiver system is configured to detect a third reflectedacoustic waveform based on a third reflection of the third emittedacoustic waveform based on the third face.

In an example implementation, a method of position sensing includesemitting a first emitted acoustic waveform through a fluid having afirst acoustic impedance toward a first acoustic interface, emitting asecond emitted acoustic waveform through the fluid toward a secondacoustic interface, reflecting, by the first acoustic interface, a firstreflected acoustic waveform based on the first emitted acousticwaveform, reflecting, by the second acoustic interface, a secondreflected acoustic waveform based on the second emitted acousticwaveform, and determining a first position of the second acousticinterface based on the first reflected acoustic waveform and the secondreflected acoustic waveform.

Various implementations can include some, all, or none of the followingfeatures. The method can include determining a first time of flightbased on the first emitted acoustic waveform and the first reflectedacoustic waveform, and determining a second time of flight based on thesecond emitted acoustic waveform and the second reflected acousticwaveform, wherein determining a first position of the second acousticinterface is further based on the first time of flight and the secondtime of flight. Determining the first position of the second acousticinterface based on the first time of flight (t1) and the second time offlight (t2) can be given by an equation: (t1−t2)/(t1+t2). The method caninclude determining a second position of the second acoustic interface,and determining a speed of the second acoustic interface based on thefirst position and the second position. The method can includedetermining a reflected acoustic frequency based on one or both of thefirst reflected acoustic waveform and the second reflected acousticwaveform, and determining a speed of the second acoustic interface basedon the determined reflected acoustic frequency and a predeterminedemitted acoustic frequency of the second emitted acoustic waveform. Thefirst acoustic interface can be defined by a first face of a fluidcavity having a second acoustic impedance that is different than thefirst acoustic impedance, the second acoustic interface can be definedby a second face of a moveable body within a fluid effector and having athird acoustic impedance that is different than the first acousticimpedance, the first emitted acoustic waveform can be emitted toward thefirst face through the fluid, the second emitted acoustic waveform canbe emitted toward the second face through the fluid, the first reflectedacoustic waveform can be based on a first reflection of the firstemitted acoustic waveform by the first face, and the second reflectedacoustic waveform can be based on a second reflection of the secondemitted acoustic waveform by the second face. The method can includedetermining a phase difference between a second emitted phase of thesecond emitted acoustic waveform and a second reflected phase of thesecond reflected acoustic waveform, wherein determining a first positionof the second acoustic interface can be further based on the determinedphase difference. The first emitted acoustic waveform can be emittedthrough a first fluid cavity toward a face of the first fluid cavitydefining the first acoustic interface, and the second emitted acousticwaveform can be emitted through a second fluid cavity toward a secondface of a moveable member defining the second acoustic interface. Thefirst emitted acoustic waveform can be emitted through a first portionof a fluid cavity toward a face of the fluid cavity defining the firstacoustic interface, and the second emitted acoustic waveform can beemitted through a second portion of the fluid cavity toward a secondface of a moveable member defining the second acoustic interface. Themethod can include emitting a third emitted acoustic waveform throughthe fluid toward a third acoustic interface, reflecting, by the thirdacoustic interface, a third reflected acoustic waveform based on thethird emitted acoustic waveform, and determining a second position ofthe third acoustic interface based on the first reflected acousticwaveform and the third reflected acoustic waveform.

In another example embodiment, a non-transitory computer storage mediumis encoded with a computer program, the computer program havinginstructions that when executed by data processing apparatus cause thedata processing apparatus to perform operations including emitting afirst emitted acoustic waveform through a fluid having a first acousticimpedance toward a first acoustic interface, emitting a second emittedacoustic waveform through the fluid toward a second acoustic interface,reflecting, by the first acoustic interface, a first reflected acousticwaveform based on the first emitted acoustic waveform, reflecting, bythe second acoustic interface, a second reflected acoustic waveformbased on the second emitted acoustic waveform, and determining a firstposition of the second acoustic interface based on the first reflectedacoustic waveform and the second reflected acoustic waveform.

The systems and techniques described here may provide one or more of thefollowing advantages. First, a system can determine a position and/orspeed of a target object though an acoustic transmission medium. Second,the system can operate without determining the acoustic properties ofthe transmission medium. Third, the system can have a more efficientand/or economical mechanical design compared to existing mechanicalposition measurement solutions such as variable differentialtransformers (VDTs). Fourth, the system can have a more efficient and/oreconomical electronic design compared to existing ultrasonic positionmeasurement solutions. Fifth, the system can provide a more spaceefficient option for system sizing. Sixth, the system can improveweight, pump demand, thermal loads, and measurement accuracy.

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features andadvantages will be apparent from the description and drawings, and fromthe claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram that shows an example of a system forultrasonic position measurement.

FIG. 2 is an internal view of an example of a linear fluid effector.

FIG. 3 is an internal view of another example of a linear fluideffector.

FIG. 4 is a sectional view of an example of an acoustic interface.

FIG. 5 is a sectional view of an example of a rotary fluid effector.

FIG. 6 is a conceptual diagram of a transmitted acoustic waveform.

FIG. 7 is a graph showing examples of phase shifts in acousticwaveforms.

FIG. 8 is a flow diagram of an example process for ultrasonic positionsensing.

FIG. 9 shows another example of a system for ultrasonic positionmeasurement.

FIG. 10 shows another example of a system for ultrasonic positionmeasurement.

FIG. 11 is a conceptual sectional view of another example linear fluideffector.

FIG. 12 is a conceptual sectional view of another example linear fluideffector.

FIG. 13 is an end view of an example transceiver.

FIG. 14 is an end view of another example transceiver.

FIG. 15 is a schematic diagram of an example fluid effector system.

FIG. 16 is a block diagram of an example transducer controller.

FIG. 17 is a block diagram of another example transducer controller.

FIG. 18 is a block diagram of time-of-flight and ratiometric functionblocks.

FIG. 19 is a graph of an example log 10 to linear transformation.

FIG. 20 is a block diagram of an example analog cross-correlationmodule.

FIG. 21 is a block diagram of an example cross-correlation receivermodule.

FIG. 22 is a schematic diagram of an example clock circuit.

FIG. 23 is a schematic of an example template generator circuit.

FIG. 24 is a graph of examples of signal timings.

FIG. 25 is a block diagram of an example closed loop control system.

FIG. 26 is a flow diagram of another example process for ultrasonicposition sensing.

FIG. 27 is a schematic diagram of an example of a generic computersystem.

DETAILED DESCRIPTION

This document describes systems and techniques for ultrasonic positionsensing, more particularly, for sensing the position of moveable membersin fluid environments, such as valve bodies and piston heads. Ingeneral, the ultrasonic position sensing systems and techniquesdescribed in this document measure the distance from a moveable objectto each end of its length of travel to determine a ratiometric positionvalue that can be determined without needing to know or otherwisedetermine the speed of sound in the medium in which the ultrasonicsignals are being transmitted.

FIG. 1 is a schematic diagram that shows an example of a system 100 forultrasonic position measurement (e.g., a position sensor system). Thesystem 100 includes a fluid effector 110. The fluid effector 110includes a housing 112 having an inner surface 114 defining a cavity 116(e.g., a cylindrical cavity), and a moveable body 118. The moveable body118 has a face 120 and a face 122 opposite the face 120, and isconfigured for reciprocal movement within the housing 112. The moveablebody 118 is configured to contact the inner surface 114 and subdividethe cavity 116 to define a fluid chamber 124 at the face 120 and definea fluid chamber 126 at the face 122, and is configured for longitudinalmovement within the cavity 116.

The fluid effector 110 includes an acoustic transceiver 130 a. Theacoustic transceiver 130 a includes an acoustic transmitter systemconfigured to emit an emitted acoustic waveform 132 a in a firstdirection toward the face 120. The acoustic transceiver 130 a alsoincludes an acoustic receiver system configured to detect a reflectedacoustic waveform 133 a based on a first reflection of the emittedacoustic waveform 132 a based on the moveable body 118. In someembodiments, a single transducer (e.g., a piezo element) can perform thefunctions of both the acoustic transmitter and the acoustic receiver. Insome embodiments, the acoustic transmitter and the acoustic receiver canbe discrete components.

The fluid effector 110 also includes an acoustic transceiver 130 b. Theacoustic transceiver 130 b includes an acoustic transmitter systemconfigured to emit an emitted acoustic waveform 132 b in a seconddirection opposite the first direction toward the face 122. The acoustictransceiver 130 a also includes an acoustic receiver system configuredto detect a reflected acoustic waveform 133 b based on a secondreflection of the emitted acoustic waveform 132 b based on the moveablebody 118. In some embodiments, a single transducer (e.g., a piezoelement) can perform the functions of both the acoustic transmitter andthe acoustic receiver. In some embodiments, the acoustic transmitter andthe acoustic receiver can be discrete components.

A signal processor 150 is configured to process signals from theacoustic transceiver 130 a and the acoustic transceiver 130 b todetermine the position of the moveable body 118 within the cavity 116. Acontroller 160 (e.g., a computer) is configured to receive positioninformation from the signal processor 150 and perform functions based onthe position information (e.g., control a process, present informationto a user, transmit information to another system, record a log). Insome embodiments, the signal processor 150 can include a timer (e.g., tomeasure the times of flight of emitted and reflected signals). In someembodiments, the signal processor 150 can include a phase detector(e.g., to determine phase and/or Doppler shifts in reflected signals).

In general, the fluid effector 110 is configured as a ratiometricposition-sensing device. A transmit-receive transducer is located oneither end of the effector. Both transmitters can send a pulse echo andreceive an echo upon reflection from the effector piston. Timemeasurements of the two transducers can independently determine theposition of a moveable body when sound speed is known. However, whencoupling two transducers into a system, sound speed is cancelled and aratiometric ultrasound position sensor is obtained. In someimplementations, if either transducer fails, redundancy can be obtainedthrough measurement or approximation of sound speed. The techniques forprocessing the signals, and several embodiments of the fluid effector110, will be discussed in the descriptions of FIGS. 2-8.

FIG. 2 is an internal view of an example of a linear fluid effector 200.In some implementations, the linear fluid effector 200 can be theexample fluid effector 110 of FIG. 1.

The fluid effector 200 includes a housing 212 having an inner surface214 defining a cavity 216 (e.g., a tubular cavity), and a moveable body218. The housing 212 is generally tubular, having a first longitudinalend 213 a and a second longitudinal end 213 b opposite the firstlongitudinal end 213 a, and a length represented by arrow 270.

The moveable body 218 has a face 220 a and a face 220 b opposite theface 220 a. The moveable body 218 is configured for reciprocal movementwithin the housing 212. The moveable body 218 is configured to contactthe inner surface 214 and subdivide the cavity 216 to define a fluidchamber 224 a on the side of the face 220 a and define a fluid chamber224 b on the side of the face 220 b.

In some embodiments, the fluid effector 200 can be configured as avalve. For example, the housing 212 can be a valve housing and themoveable body 218 can be a valve body configured to slide longitudinallywithin the valve housing to control fluid flow. In some embodiments, thefluid effector 200 can be configured as a pressure regulator or sensor,in which fluid pressure in one or both of the fluid chambers 224 a-224 bcan urge movement of the moveable body 218 within the housing. In someembodiments, the fluid effector 200 can be configured as a fluidactuator. For example, the housing 212 can be a hydraulic cylinder andthe moveable body 218 can be a piston head that can be moved within thecavity 216 to urge a fluid flow, or a piston head that can be movedwithin the cavity 216 by fluid pressure within the fluid chambers 224a-224 b. In some embodiments, the fluid effector 200 can be configuredas any appropriate form of device in which a moveable body moveslinearly within a fluid-filled cavity.

The fluid effector 200 includes an acoustic transceiver 230 a. Theacoustic transceiver 230 a includes an acoustic transmitter systemconfigured to emit an emitted acoustic waveform 232 a toward the face220 a through a medium (e.g., a fluid) filling the fluid chamber 224 a.The acoustic transceiver 230 a also includes an acoustic receiver systemconfigured to detect a reflected acoustic waveform 233 a based on areflection of the emitted acoustic waveform 232 a off the moveable body218.

The fluid effector 200 includes an acoustic transceiver 230 b. Theacoustic transceiver 230 b includes an acoustic transmitter systemconfigured to emit an emitted acoustic waveform 232 b toward the firstface 220 b through a medium filling the fluid chamber 224 b. Theacoustic transceiver 230 b also includes an acoustic receiver systemconfigured to detect a reflected acoustic waveform 233 b based on areflection of the emitted acoustic waveform 232 b off the moveable body218. In some embodiments, a single transducer (e.g., a piezo element)can perform the functions of both the acoustic transmitter and theacoustic receiver. In some embodiments, the acoustic transmitter and theacoustic receiver can be discrete components.

The acoustic transceivers 230 a-230 b are configured to be activated byan external system such as the example signal processor 150 of FIG. 1,and provide signals based on the reflected acoustic waveforms 233 a-233b to the external system for processing. In some embodiments, a singletransducer (e.g., a piezo element) can perform the functions of both theacoustic transmitter and the acoustic receiver. In some embodiments, theacoustic transmitters and the acoustic receivers can be discretecomponents.

The medium through which the acoustic waveforms 232 a and 233 a travelhas a speed of sound (C₁). In the illustrated example, the measured time(t₁) (e.g., a first time-of-flight) in conjunction with the sound speed(C₁) defines a distance L₁ (represented by arrow 260 a) from theacoustic transceiver 230 a to the face 220 a of the moveable body 218:

$\begin{matrix}{{2L_{1}} = {t_{1}*C_{1}}} & \left( {{Equation}\mspace{14mu} 1} \right)\end{matrix}$

The medium through which the acoustic waveforms 232 b and 233 b travelhas a speed of sound (C₂). In the illustrated example, the measured time(t₂) (e.g., a second time-of-flight) in conjunction with the sound speed(C₂) defines a distance L₂ (represented by arrow 260 b) from theacoustic transceiver 230 b to the face 220 b of the moveable body 218:

$\begin{matrix}{{2L_{2}} = {t_{2}*C_{2}}} & \left( {{Equation}\mspace{14mu} 2} \right)\end{matrix}$

The acoustic transceivers 230 a and 230 b and the moveable body 218 canbe configured such that the signals are used to determine a ratiometricvalue for the position of the moveable body 218 within its range ofmotion (e.g., the distance L₁+L₂, or the length 270 minus thelongitudinal thickness of the moveable body 218):

$\begin{matrix}{{Position} \sim \frac{t_{1} - t_{2}}{t_{1} + t_{2}} \sim \frac{\frac{2L_{1}}{C_{1}} - \frac{2L_{2}}{C_{2}}}{\frac{2L_{1}}{C_{1}} + \frac{2L_{2}}{C_{2}}}} & \left( {{Equation}\mspace{14mu} 3} \right)\end{matrix}$

In use, the speed of sound in the fluid that fills the cavity 216 doesnot need to be known or determined. Since both sides of the cavity 216are filled with the same type of fluid under substantially the sameconditions (e.g., temperature), the speed of sound in the fluid will bethe same on both sides of the cavity 216, and the speed of sound becomescancelled out of Equation 3. And since the speed of sound drops out ofEquation 3, the relative position of the moveable body 218 within thecavity 216 becomes a unitless ratiometric value. An absolute position ofthe moveable body 218 can be determined, if needed, based on theratiometric value and a predetermined value for the range of motion(e.g., L₁+L₂). For example, if the range of motion is known to be 10 cm,and the position is determined to be 0.63 (e.g., based on t1 and t₂),then the absolute position of the moveable body 218 within the cavity216 can be determined.

For example, the transducers may sit flush with the bore of the cylinderon both ends (e.g., if the piston head sits on the wall time is zero onthe face). In this example, if the piston is precisely in the middle,then t₁=t₂, which is 50% of stroke. However, Equation 3 isPosition˜(t₁−t₂)/(t₁+t₂)→(t₁=t₂) (e.g., the numerator goes to zero). Asthe piston strokes in one direction, t₁ decreases and t₂ increases,driving the ratio negative. Conversely, as the piston strokes in theopposite direction, the ratio increases. So at one stop the positionoutput is −1 in this example, and at the opposite stop the positionoutput is +1. In another example, for an Equation 3 measurement of 0.63this would fall between −1 (e.g., retract) and +1 (e.g., extend). Thepercentage of total stroke here becomes(0.63−(−1))/(1−(−1))→1.63/2→81.5% of total stroke. For a pistonconfiguration having a total stroke of 10 cm, the actual position fromthe housing stop would be (L₁+L₂)*81.5%=10 cm*81.5%=8.15 cm, and thedistance from the opposing stop would be 10 cm−8.15 cm=−1.85 cm.

Since the ratiometric value is based on the distances between theacoustic transceivers 230 a and 230 b and the faces 220 a and 220 b, thethickness of the moveable body 218 (e.g., the distance between the faces220 a and 220 b) does not directly affect the ratiometric value. In someimplementations, the absolute positions of the faces 220 a and 220 b canbe determined based on a determined absolute position of the moveablebody 218 and the predetermined thickness of the moveable body 218 (e.g.,the absolute position of the face 220 a-220 b can be offset from theabsolute position of the center of the moveable body 218 by plus orminus one-half the distance between the faces 220 a and 220 b or anotherpredetermined offset distance).

The described technique can be extended to perform additional functions.For example, by pinging the two sides of the moveable body 218, theposition of the moveable body 218 can be determined. By pinging the twosides of the moveable body 218 again to determine a second position ofthe moveable body, the difference in the two positions and the amount oftime between the two measurements can be used to determine a speed ofthe moveable body 218. The determined speed of the moveable body 218 andpredetermined knowledge of the mechanical configuration of the fluideffector 200 can be used to determine a linear velocity of the moveablebody 218 (e.g., the speed can be determined, and the moveable body 218is known to move linearly). In another example, multiple positionsand/or velocities can be measured and/or determined, and suchinformation can be used to determine an acceleration of the moveablebody 218.

In the example fluid effector 200, the acoustic waveforms 232 a and 232b are reflected off the faces 220 a and 220 b. The reason that theacoustic waveforms 232 a and 232 b are reflected is because the moveablebody 218 defines an acoustic interface at the faces 220 a and 220 b. Thefluid in the fluid chambers 224 a and 224 b has an acoustic impedance,and the moveable body 218 has a different acoustic impedance. As in manytypes of signal transmission systems, an impedance mismatch can cause atransmitted signal to be reflected. In the illustrated example in whichultrasonic signals are being transmitted, the locations of theseimpedance mismatches define the locations of acoustic interfaces. In theillustrated example, the face 220 a and the face 220 b define thelocations of the acoustic impedance mismatches and their correspondingacoustic interfaces. Other examples of using acoustic interfaces fordetermining the location of a moveable body are discussed in furtherdetail in the descriptions of FIGS. 3-5.

FIG. 3 is an internal view of another example of a linear fluid effector300 (e.g., a linear piston effector). In some implementations, thelinear fluid effector 300 can be the example fluid effector 110 ofFIG. 1. In general, this embodiment also relies on time of flight, butuses transverse waves propagating within the cylinder wall of theactuator instead of the hydraulic working fluid.

The linear fluid effector 300 includes a housing 312 having an innersurface 314 defining a cavity 316. A moveable body 318 (e.g., a pistonhead in the illustrated example) is configured to move longitudinallywithin the cavity 316 to actuate a piston rod 319. The housing 312 isgenerally tubular, having a first longitudinal end 313 a and a secondlongitudinal end 313 b opposite the first longitudinal end 313 a.

The moveable body 318 has a face 320 a and a face 320 b opposite theface 320 a. The moveable body 318 is configured for reciprocal movementwithin the housing 312 with a total stroke (represented by arrow 370).The moveable body 318 is configured to contact the inner surface 314 andsubdivide the cavity 316 to define a fluid chamber 324 a on the side ofthe face 320 a and define a fluid chamber 324 b on the side of the face320 b.

The linear fluid effector 300 includes an acoustic transceiver 330 a.The acoustic transceiver 330 a includes an acoustic transmitter systemconfigured to emit an emitted acoustic waveform 332 a through thehousing 312 toward a first side 320 a of an acoustic interface 321. Theacoustic transceiver 330 a also includes an acoustic receiver systemconfigured to detect a reflected acoustic waveform 333 a based on areflection of the emitted acoustic waveform 332 a off the acousticinterface 321.

The linear fluid effector 300 includes an acoustic transceiver 330 b.The acoustic transceiver 330 b includes an acoustic transmitter systemconfigured to emit an emitted acoustic waveform 332 b through thehousing 312 toward a second side 320 b of the acoustic interface 321.The acoustic transceiver 330 b also includes an acoustic receiver systemconfigured to detect a reflected acoustic waveform 333 b based on areflection of the emitted acoustic waveform 332 b off the acousticinterface 321.

The acoustic transceivers 330 a-330 b are configured to be activated byan external system such as the example signal processor 150 of FIG. 1,and provide signals based on the reflected acoustic waveforms 333 a-333b to the external system for processing. In some embodiments, a singletransducer (e.g., a piezo element) can perform the functions of both theacoustic transmitter and the acoustic receiver. In some embodiments, theacoustic transmitter and the acoustic receiver can be discretecomponents.

Transverse waves and/or surface acoustic waves are generated by acoustictransceivers 330 a-330 b located on opposing ends of the cylinder wallin intimate acoustic contact with the housing 312. In some embodiments,the acoustic transceivers 330 a-330 b can be formed of bonded bulkceramic, bulk single-crystal, or deposited piezoelectric layers,material films, or any other appropriate material that can form anintegral part of the housing 312. The acoustic transceivers 330 a-330 bare configured to generate a hoop stress in the housing 312 whichpropagates in the axial direction along the housing 312. Transversewaves and surface acoustic waves cannot propagate within fluidic masses,substantially eliminating the effects of reverberation and crosscoupling within the fluid that may otherwise interfere with measurementaccuracy. The waves are reflected when they reach the moveable body 318,being in intimate contact with the housing 312, produces an abruptacoustic impedance change in the propagation path.

In some implementations, this embodiment can be used in applicationsthat cannot accommodate transducers in contact with the hydraulic fluidmedium, cannot accommodate the required pressure ports into thehydraulic cylinder, would otherwise benefit from reduced size andlocation of the transducers, or require higher measurement accuracy thanprevious position indicators. In some implementations, sensor accuracymay not be substantially impacted compared to the echoes in the fluid.The acoustic transceivers 330 a-330 b may further be located within theinner diameter of the housing 312 in contact with the fluid, orexternally on the outside of housing 312. In some embodiments, theacoustic transceivers 330 a-330 b can be fashioned as removabletransducers. For example, the use of removable transducers can enablethe techniques described in this document to be applied or retrofittedto hydraulic or pneumatic fluidic actuators not originally designed orconceived to possess position sensing functionality at the time ofmanufacture.

The process of determining the position of the moveable member 318 issimilar to that of the process described in relation to the examplefluid effector 200 of FIG. 2, except that instead of transmitting andreceiving the acoustic waveforms 232 a, 232 b, 233 a, and 233 b thoughfluid in the fluid chambers 224 a and 224 b as in the example fluideffector 200, the acoustic waveforms 332 a, 332 b, 333 a, and 333 b aretransmitted through the housing 312. The emitted acoustic waveforms 332a and 332 b are reflected by the acoustic interface 321 as the reflectedacoustic waveforms 333 a and 333 b.

In use, the times of flight of the emitted acoustic waveforms 332 a and332 b, and their return as the reflected acoustic waveforms 333 a and333 b can be measured (e.g., times-of-flight) and used to determine theratiometric position (and by extension, the absolute position) of themoveable member 318 and the piston rod 319. For example, equations 1-3discussed above can also be used with the times-of-flight determinedfrom the linear fluid effector 300.

FIG. 4 is a sectional view of an example of an acoustic interface 400.In some examples, the acoustic interface 400 can be the example acousticinterface 321 of FIG. 3. In the illustrated example, a housing 412includes an inner surface 414 that defines a cavity 416. A seal 419 isconfigured to contact the inner surface 414 and a moveable body 418 tosubdivide the cavity 416 into a fluid chamber 424 a and a fluid chamber424 b. The seal 419 contacts the housing 412 at a contact area 420.

Acoustic impedance is defined as Z=ρ_(B)V_(P), where P_(B) is the bulkdensity of the medium and is the longitudinal velocity of the wave inthe medium. The housing 412 is made out a material that has a naturalacoustic impedance, for example, due to the temperature, density, andother properties of the material from which the housing 412 is formed.In the illustrated example, the regions of the housing 412 having thenatural acoustic impedance are represented by a light dither pattern andthe identifier 450. For example, the acoustic impedance of aluminum isabout 17.10 g/cm²-sec×10⁵, and the acoustic impedance of 347 stainlesssteel is about 45.40 g/cm²-sec×10⁵. These are just two examples ofacoustic impedances for two different materials. The techniquesdescribed in this document make it unnecessary to know, determine, orestimate the acoustic impedance of a material.

The housing 412 also includes a region of modified acoustic impedancerepresented by a denser dither pattern and the identifier 460. In someembodiments, the effective acoustic impedance of a material can beaffected by mechanical contact with or proximity to another object at oraround the point of contact or proximity. For example, mechanicalcontact between the seal 419 and the housing 412 can acoustically dampenthe housing 412 at or around the contact area 420 and increase theacoustic density of the housing 412 at or near the contact area 420. Insuch examples, the region 460 can have a relatively higher acousticimpedance than the regions 450. In another example, the seal 419 mayhave a lower acoustic impedance than the housing 412, and mechanicalcontact between the seal 419 and the housing 412 can provide a path oflesser acoustic impedance for acoustic vibrations travelling along thehousing 412 at or near the contact area 420, effectively lowering theacoustic impedance of the acoustic transmission pathway in the region460 relative to the regions 450.

In general, when two sections of a transmission medium have differentimpedances, an impedance mismatch is presented. The boundaries betweendiffering acoustic impedances define the locations of acoustic impedancemismatches, which are also called acoustic interfaces. In theillustrated example, acoustic waves traverse at the interface of thefluid and the housing (e.g., along the inner surface 414). The mismatchin impedance occurs when the fluid becomes the seal. The junctions wherethe inner surface 414, the fluid, and the seal 419 coincide one anotherdefine an acoustic interface 470 a and an acoustic interface 470 b.

As in many types if signal transmission processes, a signal thatpropagates along a transmission pathway and then encounters an impedancemismatch can result in at least a portion of the signal to be reflectedback along the transmission pathway. Similarly, acoustic signals (e.g.,the emitted acoustic waveforms 332 a and 332 b) can be reflected backtoward their sources by acoustic interfaces.

In the illustrated example, the locations of the acoustic interfaces 470a and 470 b within the housing 412 are defined by the location of themoveable body 418 within the cavity 416 (e.g., the moveable body 418defines the location of the seal 419, which defines the location of theregion 460, which defines the locations of the acoustic interfaces 470 aand 470 b). Movement of the moveable body 418 causes the acousticinterfaces 470 a and 470 b to move as well.

Returning briefly to FIG. 3, movement of the moveable body 318 causescorresponding movements of acoustic interfaces (e.g., the acousticinterfaces 470 a and 470 b) within the housing 312. As the moveable body318 moves, the distances between the acoustic transceivers 330 a and 330b and their respective acoustic interfaces change as well, which causesproportional changes in the times-of-flight of the emitted acousticwaveforms 332 a and 332 b and the reflected acoustic waveforms 333 a and333 b. As discussed above, the times of flight can be used to determinethe ratiometric position of the acoustic interfaces along the housing312, and therefore determine the position of the moveable member 318within the cavity 316. As also discussed above, these locations can bedetermined without knowing or determining the acoustic properties of thehousing (e.g., the acoustic impedances of the housing or of regions ofmodified acoustic impedance, which can change dynamically withtemperature).

FIG. 5 is a sectional view of an example of a rotary fluid effector 500.In some implementations, the rotary fluid effector 500 can be theexample fluid effector 110 of FIG. 1. The rotary fluid effector 500includes a housing 512 having an inner surface 514 defining a cavity 516that is generally cylindrical. A moveable body 518 (e.g., a rotary vanein the illustrated example) is configured to move semi-elliptically(e.g., rotate, pivot) about a central axis 511 of a shaft 519 within thecavity 516. In some embodiments, the moveable body 518 can be configuredto urge rotation of the shaft 519.

The moveable body 518 is configured to contact the inner surface 514(e.g., directly or through a seal) along a contact area 520 at or alongan axial position of the generally cylindrical housing 512. Thematerials used to form the housing 512 have an acoustic impedance, andthe contact between the moveable body 518 and the housing 512 modifiedthe acoustic impedance of the housing 512 at or around the contact area520 to define a region 560 having a modified acoustic impedance. Theregion 560 presents an acoustic impedance mismatch within the housing512, having an acoustic interface 570 a and an acoustic interface 570 b.

The rotary fluid effector 500 includes an acoustic transceiver 530. Theacoustic transceiver 530 includes an acoustic transmitter systemconfigured to emit an emitted acoustic waveform 532 a through thehousing 512 toward the acoustic interface 570 a. The acoustictransceiver 530 also includes an acoustic receiver system configured todetect a reflected acoustic waveform 533 a based on a reflection of theemitted acoustic waveform 532 a off the acoustic interface 570 a.

The acoustic transceiver 530 is also configured to emit an emittedacoustic waveform 532 b through the housing 512 toward the acousticinterface 570 b of the region 560. The acoustic transceiver 530 alsoincludes an acoustic receiver system configured to detect a reflectedacoustic waveform 533 b based on a reflection of the emitted acousticwaveform 532 b off the acoustic interface 570 b. In the illustratedexample, the acoustic transceiver 530 is configured to perform thetransmission and receipt of the acoustic waveforms 532 a, 532 b, 533 a,and 533 b (e.g., by “ringing” the housing 512 at a single location andhaving the emitted waveforms 532 a-532 b propagate away from bothsides), but in some embodiments separate acoustic transceivers can beused (e.g., one configured to ring the periphery of the housing 512 in aclockwise direction and another configured to ring the periphery in acounter-clockwise direction).

The acoustic transceiver 530 is configured to be activated by anexternal system such as the example signal processor 150 of FIG. 1, andprovide signals based on the reflected acoustic waveforms 533 a-533 b tothe external system for processing. In some embodiments, a singletransducer (e.g., a piezo element) can perform the functions of both theacoustic transmitter and the acoustic receiver. In some embodiments, theacoustic transmitter and the acoustic receiver can be discretecomponents.

The process of determining the position of the moveable body 518 issimilar to that of the process described in relation to the examplelinear fluid effector 300 of FIG. 3, except that instead of transmittingand receiving the acoustic waveforms 332 a, 332 b, 333 a, and 333 balong the longitudinal length of the housing 312 as in the examplelinear fluid effector 300, the acoustic waveforms 532 a, 532 b, 533 a,and 533 b are transmitted circumferentially (e.g., orbitally) about thehousing 512. The emitted acoustic waveforms 532 a and 532 b arereflected by the acoustic interface 521 as the reflected acousticwaveforms 533 a and 533 b.

In use, the times of flight of the emitted acoustic waveforms 532 a and532 b, and their return as the reflected acoustic waveforms 533 a and533 b can be measured (e.g., times-of-flight) and used to determine theratiometric position (and by extension, the absolute position) of themoveable body 518 and the shaft 519. For example, equations 1-3discussed above can also be used with the times-of-flight determinedfrom the rotary fluid effector 500.

In some embodiments, the rotary fluid effector 500 can be a rotary vaneactuator (RVA) or a rotary valve. In some embodiments, the rotary fluideffector can be modified to be a rotary piston actuator (RPA). Forexample, emitted waveforms can be transmitted circumferentially about atubular housing toward the end of a rotary piston that is configured tomove about the axis of the housing and define an acoustic interfacewithin a portion of the housing, and the acoustic interface can reflecta portion of the waveforms for use in determining the rotary position ofthe rotary piston.

FIG. 6 is a conceptual diagram 600 of a transmitted acoustic waveform610. FIG. 7 is a graph 700 showing examples of phase shifts in acousticwaveforms. In addition to time based measurement (e.g., as discussedabove), time and phase are related to one another as a function offrequency and wavelength. In the illustrated example, the transmittedacoustic waveform 610 is transmitted by an acoustic transceiver 620 as acontinuous wave of single frequency f. The transmitted acoustic waveform610 is broadcast toward a moveable reflector 630 positioned at somedistance D from the reflector. The transmitted acoustic waveform 610 isreflected back toward the acoustic transceiver 620, and reaches theacoustic transceiver 620 after making a round trip of length L=2D.

The acoustic transceiver 620 travels some whole number n of wavelengthsplus a fraction, where wavelength is given by:

$\begin{matrix}{{\lambda = {{{c/f}\mspace{14mu}{where}\mspace{14mu} c} = {{sound}\mspace{14mu}{speed}}}},{f = {{wave}\mspace{14mu}{frequency}}}} & \left( {{Equation}\mspace{14mu} 4} \right)\end{matrix}$

Using Equation 4, the round trip distance to target can be written as:

$\begin{matrix}{D = {\left( {n_{1} + \frac{\phi}{2\pi}} \right) \times \frac{\lambda}{2}}} & \left( {{Equation}\mspace{14mu} 5} \right) \\{\phi_{1} = {{2\pi\; f_{1}T_{1}} = \frac{4\pi\; f_{1}d_{1}}{c}}} & \left( {{Equation}\mspace{14mu} 6} \right) \\{T_{1} = \frac{\phi_{1}}{2\pi\; f_{1}}} & \left( {{Equation}\mspace{14mu} 7} \right) \\{\phi_{2} = {{2\pi\; f_{2}T_{2}} = \frac{4\pi\; f_{2}d_{2}}{c}}} & \left( {{Equation}\mspace{14mu} 8} \right) \\{T_{2} = \frac{\phi_{2}}{2\pi\; f_{2}}} & \left( {{Equation}\mspace{14mu} 9} \right)\end{matrix}$

Where the ϕ/2π term is equivalent to time as shown in Equations 7 and 9.If n₁=0, Equation 2 is unambiguous and since the frequency f and fluidsound speed are known apriori, D can be determined by direct measurementof the phase of the received signal relative to the transmitted signal.

When n₁>1, D is ambiguous as the measured phase values repeat atintervals of 2πf. The value n₁ can be extracted from the measured databased on the idea that the differential phase shift of twosimultaneously propagating waves of differing frequencies will generateprogressively larger phase shifts; the value of the increase is aconstant φ_(d) as the travel time increases. This is shown in FIG. 7.Detecting the two signals at some distance D and knowing they begantraveling at the same time the measured phase can be divided by φ_(d) toextract the number of complete wave periods that occurred to generatethe measured phase difference. Mathematically:

$\begin{matrix}{{{\phi_{1} - \phi_{2}}} = {{D\left( {\frac{1}{\lambda_{1}} - \frac{1}{\lambda_{2}}} \right)} = \frac{\Delta\;\phi}{2\pi}}} & \left( {{Equation}\mspace{14mu} 10} \right)\end{matrix}$

The phase difference embodiment modifies the time difference embodimentby applying a fixed frequency f₁ to the phase measurement in one of thefluid chambers, and another fixed frequency f₂ to the other fluidchamber. The exact frequency values of f₁ and f₂ are not critical to thefunction of the invention, however it is critical that the frequenciesare selected to ensure that n₁=n₂ or n₁=n₂+1. This relationship ensuresthat the value of god remains constant over the entire measurementrange.

Rewriting Equation 3, using Equations 7 and 9:

$\begin{matrix}{{{Stroke} \sim \frac{t_{1} - t_{2}}{t_{1} + t_{2}} \sim \frac{\frac{\phi_{1}}{2\pi\; f_{1}} - \frac{\phi_{2}}{2\pi\; f_{2}}}{\frac{\phi_{1}}{2\pi\; f_{1}} + \frac{\phi_{2}}{2\pi\; f_{2}}}} = \frac{{\phi_{1} - {\frac{f_{1}}{f_{2}}\phi_{2}}}}{{\phi_{1} + {\frac{f_{1}}{f_{2}}\phi_{2}}}}} & \left( {{Equation}\mspace{14mu} 11} \right)\end{matrix}$

The phase embodiment maintains the same ratiometric benefits ofmechanical length and sound speed insensitivity as the time of flightembodiment. The frequency f₁ is related to f₂ by a fixed ratio. Thiscondition ensures the relative phase difference remains constant withcircuit aging and temperature change. Other embodiments can remove thisrestriction with the result of reduced aging performance and temperaturecompensation without substantively altering the method.

Ultrasonic pulses are emitted periodically as is prescribed for positionmeasurement. Following each emission, the returned echo signal issampled at a fixed delay after the emission. From Equations 13 and 14,this delay defines the depth.

As the actuator moves between the successive emissions the sampledvalues taken at time T_(s) will change over the time. As the speedinformation is available only periodically, the technique is limited bythe Nyquist theorem. This means that a maximum speed exists for eachpulse repetition frequency (F_(prf)):

$\begin{matrix}{V_{\max} = \frac{F_{prf}*C}{4*F_{e}*\cos\delta}} & \left( {{Equation}\mspace{14mu} 12} \right)\end{matrix}$

The maximum measurable depth is also defined by the pulsed repetitionfrequency:

$\begin{matrix}{P_{\max} = \frac{C}{2*F_{prf}}} & \left( {{Equation}\mspace{14mu} 13} \right)\end{matrix}$

Therefore the product of P_(max) and V_(max) is constant, and is givenby:

$\begin{matrix}{{P_{\max}*V_{\max}} = \frac{C^{2}}{8*F_{s}*\cos\delta}} & \left( {{Equation}\mspace{14mu} 14} \right)\end{matrix}$

FIG. 8 is a flow diagram of an example process 800 for ultrasonicposition sensing. In some implementations, the process 800 can beperformed by all or part of the example system 100 of FIG. 1, theexample fluid effector 110, the example linear fluid effector 200 ofFIG. 2, the example linear fluid effector 300 of FIG. 3, or the examplerotary fluid effector 500 of FIG. 5.

At 810, a first emitted acoustic waveform is emitted in a firstdirection through an acoustic medium having a first acoustic impedancetoward a first side of an acoustic interface. For example, the acoustictransceiver 130 a can emit the emitted acoustic waveform 132 a towardthe face 120 of the moveable body 118 through a fluid in the cavity 116.In another example, the acoustic transceiver 530 can emit the emittedacoustic waveform 532 a toward the acoustic interface 570 a of themoveable body 518 through the housing 512.

At 820, a second emitted acoustic waveform is emitted in a seconddirection, opposite the first direction, through the acoustic mediumtoward a second side of the acoustic interface opposite the first side.For example, the acoustic transceiver 130 b can emit the emittedacoustic waveform 132 b toward the face 122 of the moveable body 118through a fluid in the cavity 116. In another example, the acoustictransceiver 530 can emit the emitted acoustic waveform 532 b toward theacoustic interface 570 b through the housing 512.

At 830, a first reflected acoustic waveform is reflected by the acousticinterface in the second direction based on the first emitted acousticwaveform. For example, the face 120 can reflect the reflected acousticwaveform 133 a back toward the acoustic transceiver 130 a. In anotherexample, the acoustic interface 570 a can reflect the reflected acousticwaveform 533 a back toward the acoustic transceiver 530.

At 840, a second reflected acoustic waveform is reflected by theacoustic interface in the first direction based on the second emittedacoustic waveform. For example, the face 122 can reflect the reflectedacoustic waveform 133 b back toward the acoustic transceiver 130 b. Inanother example, the acoustic interface 570 b can reflect the reflectedacoustic waveform 533 b back toward the acoustic transceiver 530.

At 850, a first position of the acoustic interface is determined basedon the first reflected acoustic waveform and the second acousticwaveform. For example, measurements based on the emitted acousticwaveforms 132 a, 132 b, 133 a, and 133 b, or the acoustic waveforms 532a, 532 b, 533 a, and 533 b can be used with Equations 1-14 to determinethe positions of the moveable bodies 118 or 518.

In some implementations, the process 800 can also include determining afirst time of flight based on the first emitted acoustic waveform andthe first reflected acoustic waveform, and determining a second time offlight based on the second emitted acoustic waveform and the secondreflected acoustic waveform, where determining a first position of theacoustic interface is further based on the first time of flight and thesecond time of flight. In some implementations, determining the firstposition of the acoustic interface based on the first time of flight(t₁) and the second time of flight (t₂) is given by an equation:(t₁−t₂)/(t₁+t₂). For example, Equation 3 shows an example of how timesof flight of reflected acoustic waveforms can be used to determine aratiometric position of the acoustic interface that caused thereflections.

In some implementations, the process 800 can also include determining asecond position of the acoustic interface, and determining a speed ofthe acoustic interface based on the first positon and the secondposition. For example, by determining a first position of the moveablebody 118, a second position of the moveable body 118, and the amount oftime between the two positions, a speed at which the moveable body 118is moving can be determined.

In some implementations, the process 800 can include determining areflected acoustic frequency based on one or both of the first reflectedacoustic waveform and the second acoustic waveform, and determining aspeed of the acoustic interface based on the determined reflectedacoustic frequency and a predetermined emitted acoustic frequency of oneor both of the first emitted acoustic waveform and the second emittedacoustic waveform. For example, the emitted acoustic waveforms 132 a and132 b can be emitted at a predetermined emitted frequency, and movementof the example moveable body 118 can cause a Doppler shift in thereflected acoustic waveforms 133 a and 113 b. The degree of the Dopplershift can be measured to determine a speed of the moveable body 118relative to the acoustic transceivers 130 a and 130 b.

In some implementations, the acoustic medium can be a fluid having afirst acoustic impedance, the acoustic interface can be defined by amoveable body within a fluid effector and having a second acousticimpedance that is different than the first acoustic impedance, the firstemitted acoustic waveform can be emitted toward a first face of themoveable body through the fluid, the second emitted acoustic waveformcan be emitted toward a second face of the moveable body, arrangedopposite the first face, through the fluid, the first reflected acousticwaveform can be based on a first reflection of the first emittedacoustic waveform by the first face, and the second reflected acousticwaveform can be based on a second reflection of the second emittedacoustic waveform by the second face. For example, the emitted acousticwaveforms 132 a and 132 b can travel through a fluid in the cavity 116to the face 120 and the face 122, and be reflected back through thefluid to the acoustic transceivers 130 a and 130 b.

In some implementations, the acoustic medium can be a housing of a fluideffector, the housing having a first acoustic impedance and defining acavity, and also including contacting a portion of the housing with amoveable body configured for movement within the cavity, and modifying,based on the contacting, the first acoustic impedance of the contactedportion of the housing to define a portion of the housing having asecond acoustic impedance that is different from the first acousticimpedance, where the contacted portion of the housing defines theacoustic interface. For example, contact between the example seal 419and the example housing 412 can develop the region of modified acousticimpedance 460.

In some implementations, the process 800 can also include determining aphase difference between at least one of (1) a first emitted phase ofthe first emitted acoustic waveform and a first reflected phase of thefirst reflected acoustic waveform, and (2) a second emitted phase of thesecond emitted acoustic waveform and a second reflected phase of thesecond reflected acoustic waveform, wherein determining a first positionof the acoustic interface is further based on the determined phasedifference. For example, the differences in phase between the emittedacoustic waveform 132 a and the reflected acoustic waveform 133 a can beused (e.g., in the example Equations 4-14) to determine a position ofthe moveable body 118.

All of the embodiments described can provide, in addition to position,direct measurement of actuator speed by the incorporation of signalprocessing to extract Doppler shift information (e.g., reflectedfrequency) from the transducer(s) signals. While only one of theplurality of transducers is required to be processed, Doppler processingof two transducers can provide higher accuracy by a factor of about 1.4×over the use of a single channel.

FIG. 9 shows an example of a system 900 for ultrasonic positionmeasurement (e.g., a position sensor system). The system 900 includes afluid effector 910. The fluid effector 910 includes a sensor housing 912defining a cavity 920 having a face 922. The fluid effector 910 alsoincludes an actuator housing 914 having an inner surface 931 defining acavity 930. The cavities 920 and 930 are fluidically connected by apassage 980. A moveable body 938 is configured for reciprocal movementwithin the cavity 930. The moveable body 938 has a face 932.

In the illustrated example, the sensor housing 912 and the actuatorhousing 914 are a unified housing that includes both of the cavities 920and 930. As will be discussed in the description of FIG. 15, the sensorhousing and the actuator housing may be separate housings.

The system 900 includes an acoustic transceiver 940 a that is configuredas an acoustic transmitter or acoustic emitter to emit an emittedacoustic waveform 942 a toward the face 922. The acoustic transceiver940 a is also configured as an acoustic receiver configured to detect areflected acoustic waveform 944 a based on a reflection of the emittedacoustic waveform 942 a off the face 922. In some embodiments, a singletransducer (e.g., a piezo element) can perform the functions of both theacoustic transmitter and the acoustic receiver. In some embodiments, theacoustic transmitter and the acoustic receiver can be discretecomponents.

The system 900 includes an acoustic transceiver 940 b that is configuredas an acoustic transmitter or acoustic emitter to emit an emittedacoustic waveform 942 b toward the face 932. The acoustic transceiver940 b is also configured as an acoustic receiver configured to detect areflected acoustic waveform 944 b based on a reflection of the emittedacoustic waveform 942 b off the face 932. In some embodiments, a singletransducer (e.g., a piezo element) can perform the functions of both theacoustic transmitter and the acoustic receiver. In some embodiments, theacoustic transmitter and the acoustic receiver can be discretecomponents.

A signal processor 960 is configured to process signals from theacoustic transceiver 940 a and the acoustic transceiver 940 b todetermine the position of the moveable body 938 within the cavity 930. Acontroller 970 (e.g., a computer) is configured to receive positioninformation from the signal processor 960 and perform functions based onthe position information (e.g., control a process, present informationto a user, transmit information to another system, record a log). Insome embodiments, the signal processor 960 can include a timer (e.g., tomeasure the times of flight of emitted and reflected signals). In someembodiments, the signal processor 960 can include a phase detector(e.g., to determine phase and/or Doppler shifts in reflected signals).

In general, the fluid effector 910 is configured as a ratiometricposition-sensing device. The acoustic transceiver 940 a is configured tosound a known, fixed distance 950 a to the face 922, whereas theacoustic transceiver 940 b is configured to sound the variable distance950 b to the face 932 of the moveable body 938. Time measurements of thetwo acoustic transceivers 940 a, 940 b can be used to determine theposition of the moveable body 938 when sound speed is known. However,when coupling two transducers into a system, sound speed is cancelledand a ratiometric ultrasound position sensor is obtained. The passage980 is provided to improve equalization of fluid temperatures in thecavities 920, 930 to improve equalization of the speed of sound in thefluids that occupy the cavities 920, 930. In some implementations, ifeither transducer fails, redundancy can be obtained through measurementor approximation of sound speed. The techniques for processing thesignals, and several embodiments of the fluid effector 910, will bediscussed in the descriptions of FIGS. 16-26.

In the illustrated example shown in FIG. 9, the fluid effector isconfigured as a linear (e.g., piston) actuator. FIG. 10 shows anotherexample of a system 1000 for ultrasonic position measurement. The system1000 is substantially similar to the example system 900, except thesystem 1000 includes a fluid effector 1010 that is configured as avalve.

The fluid effector 1010 includes the sensor housing 1012 defining acavity 1020 having a face 1022. The fluid effector 1010 also includes anactuator housing 1014 having an inner surface 1031 defining a cavity1030. A moveable body 1038 is configured for reciprocal movement withinthe cavity 1030. The moveable body 1038 has a face 1032. In theillustrated example, the moveable body 1038 is configured as a valvebody.

In the illustrated example, the sensor housing 1012 and the actuatorhousing 1014 are a unified housing that includes both of the cavities1020 and 1030. As will be discussed in the description of FIG. 15, thesensor housing and the actuator housing may be separate housings.

The system 1000 includes an acoustic transceiver 1040 a that isconfigured as an acoustic transmitter or acoustic emitter to emit anemitted acoustic waveform 1042 a toward the face 1022. The acoustictransceiver 1040 a is also configured as an acoustic receiver configuredto detect a reflected acoustic waveform 1044 a based on a reflection ofthe emitted acoustic waveform 1042 a off the face 1022. In someembodiments, a single transducer (e.g., a piezo element) can perform thefunctions of both the acoustic transmitter and the acoustic receiver. Insome embodiments, the acoustic transmitter and the acoustic receiver canbe discrete components.

The system 1000 includes an acoustic transceiver 1040 b that isconfigured as an acoustic transmitter or acoustic emitter to emit anemitted acoustic waveform 1042 b toward the face 1032. The acoustictransceiver 1040 b is also configured as an acoustic receiver configuredto detect a reflected acoustic waveform 1044 b based on a reflection ofthe emitted acoustic waveform 1042 b off the face 1032. In someembodiments, a single transducer (e.g., a piezo element) can perform thefunctions of both the acoustic transmitter and the acoustic receiver. Insome embodiments, the acoustic transmitter and the acoustic receiver canbe discrete components.

A signal processor 1060 is configured to process signals from theacoustic transceiver 1040 a and the acoustic transceiver 1040 b todetermine the position of the moveable body 1038 within the cavity 1030.A controller 1070 (e.g., a computer) is configured to receive positioninformation from the signal processor 1060 and perform functions basedon the position information (e.g., control a process, presentinformation to a user, transmit information to another system, record alog). In some embodiments, the signal processor 1060 can include a timer(e.g., to measure the times of flight of emitted and reflected signals).In some embodiments, the signal processor 1060 can include a phasedetector (e.g., to determine phase and/or Doppler shifts in reflectedsignals).

FIG. 11 is a conceptual sectional view of an example linear fluideffector 1100. In the illustrated example, the effector 1100 is definedby a housing 1102 with an inner surface 1104 that defines a cavity 1106.

A moveable member 1110 is configured for axial movement within a portion1120 of the cavity 1106. The portion 1120 is sized to contact themoveable body 1110 and partly define a fluid chamber having across-sectional area 1121, and can be pressurized to urge linearmovement of the moveable body 1110.

A portion 1122 of the cavity 1106 is arranged axially adjacent to theportion 1120, and has an axial cross-sectional area 1123 that is largerthan the cross-sectional area 1121 of the portion 1120. A face portion1130 is defined by an axial shoulder transition between thecross-sectional area 1121 and the cross-sectional area 1123.

The portion 1120 and the portion 1122 together define a unified cavityin which fluid (e.g., fuel) is free to move between the portions 1120,1122 and maintain a substantially even distribution of temperaturesthroughout the cavity 1106. In the illustrated example, the portion 1122is coaxially larger than the portion 1120 in cross-section. In someembodiments, the portion 1122 may be axially offset asymmetrically fromthe portion 1122. In some embodiments, the portion 1122 may be at leastpartly discontinuous from the portion 1120.

An acoustic transceiver 1140 is arranged at an axial end of the housing1102. The acoustic transceiver 1140 is configured to emit an emittedacoustic signal 1150 toward both the moveable body 1110 and the faceportion 1130. The face portion 1130 reflects a portion of the emittedacoustic signal 1150 back toward the acoustic transceiver 1140 as areflected acoustic signal 1152. The face portion 1112 of the moveablebody 1110 reflects another portion of the emitted acoustic signal 1150back toward the acoustic transceiver 1140 as a reflected acoustic signal1154.

In operation, a signal processor (e.g., the example signal processor 960of FIG. 9) can activate the acoustic transceiver 1140 to emit theemitted acoustic signal 1150 and use the acoustic transceiver 1140 tosense the reflected acoustic signals 1152 and 1154. The signal processorcan determine a time of flight for both the reflected acoustic signals1152 and 1154 to determine the position of the moveable body 1110 withinthe cavity 1106. The techniques for processing the signals will bediscussed in the descriptions of FIGS. 16-26.

FIG. 12 is a conceptual sectional view of another example linear fluideffector 1200. In general, the linear fluid effector 1200 is amodification of the example linear fluid effector 1100 of FIG. 11, inwhich the acoustic transceiver 1140 has been replaced by an acoustictransceiver 1240.

FIG. 13 is an end view of the example acoustic transceiver 1240 of FIG.12. The acoustic transceiver 1240 includes an acoustic transceiverportion 1242 that at least partly coaxially surrounds an acoustictransceiver portion 1244. The acoustic transceiver portion 1242 is sizedbased on the cross-sectional area 1123, and the acoustic transceiverportion 1244 is sized based on the cross-sectional area 1121. Theacoustic transceiver portion 1244 is configured to emit an emittedacoustic signal 1250 toward the moveable body 1110, and the acoustictransceiver portion 1242 is configured to emit an emitted acousticsignal 1251 toward the face portion 1130. The face portion 1130 reflectsa portion of the emitted acoustic signal 1251 back toward the acoustictransceiver portion 1242 as a reflected acoustic signal 1252. The faceportion 1112 of the moveable body 1110 reflects a portion of the emittedacoustic signal 1250 back toward the acoustic transceiver portion 1244as a reflected acoustic signal 1254.

The acoustic transceiver portions 1242, 1244 are separately operable andreadable by a signal processor (e.g., the example signal processor 960of FIG. 9). The signal processor can determine a time of flight for boththe reflected acoustic signals 1252 and 1254 to determine the positionof the moveable body 1110 within the cavity 1106. The techniques forprocessing the signals will be discussed in the descriptions of FIGS.16-26.

FIG. 14 is an end view of another example acoustic transceiver 1400. Insome embodiments, the acoustic transceiver 1400 can be substituted forthe example acoustic transceiver 1240 of FIGS. 12-13.

The acoustic transceiver 1400 includes an acoustic transceiver portion1242 that is radially offset from an acoustic transceiver portion 1444.The acoustic transceiver portion 1442 is sized based on thecross-sectional area 1121, and the acoustic transceiver portion 1444 issized based on the cross-sectional area 1123. The acoustic transceiverportion 1444 is configured to emit an emitted acoustic signal toward theexample moveable body 1110, and the acoustic transceiver portion 1442 isconfigured to emit an emitted acoustic signal toward the example faceportion 1130. The face portion 1130 reflects a portion of the acousticsignal emitted by the acoustic transceiver portion 1442 back toward theacoustic transceiver portion 1442 as a reflected acoustic signal. Theface portion 1112 of the moveable body 1110 reflects a portion of theacoustic signal emitted by the acoustic transceiver portion 1444 backtoward the acoustic transceiver portion 1444 as a reflected acousticsignal.

The acoustic transceiver portions 1442, 1444 are separately operable andreadable by a signal processor (e.g., the example signal processor 960of FIG. 9). The signal processor can determine a time of flight for boththe reflected acoustic signals to determine the position of the moveablebody 1110 within the cavity 1106. The techniques for processing thesignals will be discussed in the descriptions of FIGS. 16-26.

The acoustic transceiver 1440 also includes an acoustic transceiverportion 1446 that is radially offset from an acoustic transceiverportion 1444. The acoustic transceiver portion 1444 is sized based onthe cross-sectional area 1123. The acoustic transceiver portion 1446 isconfigured to emit an emitted acoustic signal toward the example faceportion 1130. The face portion 1130 reflects a portion of the acousticsignal emitted by the acoustic transceiver portion 1446 back toward theacoustic transceiver portion 1446 as a reflected acoustic signal. Insome embodiments, the acoustic transceiver portions 1442 and 1146 arepart of a single acoustic transceiver device that is separately operableand measurable from the acoustic transceiver portion 1444. In someembodiments, the acoustic transceiver portion 1446 is separatelyoperable and measurable from the acoustic transceiver portion 1442 and1144. For example, the acoustic transceiver portion 1446 can be usedredundantly in cooperation with the acoustic transceiver portion 1442.

FIG. 15 is a schematic diagram of an example fluid effector system 1500.The system 1500 includes an acoustic fluid measurement module 1502 a andan acoustic fluid measurement module 1502 b. Each of the acoustic fluidmeasurement modules 1502 a, 1502 b includes a sensor housing 1504 thatdefines a cavity 1505 having a predetermined length and a face 1507, andan acoustic transceiver 1506 configured to perform a time-of-flightmeasurement of the length of the cavity 1505. The acoustic fluidmeasurement modules 1502 a, 1502 b are operable and readable by a signalprocessor 1560 and a controller 1570 to determine time of flight ofacoustic signals within the acoustic fluid measurement modules 1502 a,1502 b. In some embodiments, the acoustic fluid measurement modules 1502a, 1502 b can provide functionality similar to that of the exampleacoustic transceivers 940 a and/or 1040 a of FIGS. 9 and 10.

The system 1500 also includes a collection of fluid effectors 1510a-1510 c, each having an actuator housing 1512 defining a cavity 1516 inwhich a moveable body 1514 having a face 1517 is configured to moveaxially. In various embodiments, each of the fluid effectors 1510 a-1510c can be any appropriate form of fluid effector, such as a linear fluidactuator or a fluid actuated valve. Each of the fluid effectors 1510a-1510 c also includes an acoustic transceiver 1518 configured toperform a time-of-flight measurement of the length of the cavity 1516.The acoustic transceivers 1518 are operable and readable by the signalprocessor 1560 and the controller 1570 to determine times of flights ofacoustic signals within fluid effectors 1510 a-1510 c. In someembodiments, the acoustic transceivers 1518 can provide functionalitysimilar to that of the example acoustic transceivers 940 b and/or 1040 bof FIGS. 9 and 10.

In the illustrated example, the system 1500 is shown with two acousticfluid measurement modules and three fluid effectors, though anyappropriate number of one or more acoustic fluid measurement modules andany appropriate number of one or more fluid effectors can be used. Forexample, a single acoustic fluid measurement module can be used toprovide a baseline measurement, or multiple acoustic fluid measurementmodules can be used to provide redundancy. In another example, one ormore baseline measurements from one or a collection of acousticmeasurement modules can be used with one, two, three, five, ten, twenty,or any other appropriate number of fluid effectors.

In very general terms, the acoustic fluid measurement modules 1502 a,1502 b can be used to provide (e.g., redundant) baseline measurementsagainst which the measurements by the acoustic transceivers 1518 can becompared to determine the positions of the moveable bodies 1514. Inoperation, operative fluid (e.g., fuel) flows along a supply passage1540, through the acoustic fluid measurement modules 1502 a, 1502 b tothe fluid effectors 1510 a-1510 c, and out through a return passage1542. The signal processor 1560 can activate the acoustic transceivers1506 to emit emitted acoustic signals and use the acoustic transceivers1506 to sense the reflected acoustic signals. The signal processor candetermine a time of flight of the reflected acoustic signals within theknown lengths of the cavities 1505. The signal processor 1560 canactivate the acoustic transceivers 1518 to emit emitted acoustic signalsand use the acoustic transceivers 1518 to sense the reflected acousticsignals to determine the times of flights of the signals due to thepositions of the moveable bodies 1514 within the cavities 1516. Thesignal processor 1560 can compare the times of flights from the acousticfluid measurement modules 1502 a, 1502 b to the times of flights fromthe fluid effectors 1510 a-1510 c to determine the positions of themoveable bodies 1514 within the cavities 1516. The techniques forprocessing the signals will be discussed in the descriptions of FIGS.16-26.

FIGS. 16-26 show examples of various systems that can be used to performpositional measurement and control using apparatus such as the examplesshown and described above.

To improve system sizing, two ultrasound sensors are implemented oneither chamber of a fluid effector. The ultrasound sensor transmits asignal which reflects off the effector and is received by thetransducer. The measured time in conjunction with the sound speeddefines the distance to the effector (see Equation 1). When coupling twotransducers together the other chamber follows the same form (seeEquation 2).

The transducers and the effector can be configured such that the signalsare used as a ratio metric device, rather:

$\begin{matrix}{{Stroke} \sim \frac{t_{1} - t_{2}}{t_{1} + t_{2}} \sim \frac{\frac{L_{1}}{C_{1}} - \frac{L_{2}}{C_{2}}}{\frac{L_{1}}{C_{1}} + \frac{L_{2}}{C_{2}}}} & \left( {{Equation}\mspace{14mu} 15} \right)\end{matrix}$

Since C₁˜C₂, as a ratio metric device, the effects of sound speedcharacteristics are cancelled out and not required for evaluation ofposition. In addition to time based measurement, time, and phase arerelated to one another as a function of frequency and wavelength. Acontinuous wave of single frequency f is broadcast toward a moveablereflector positioned at some distance D from the reflector. The wave isreflected back toward the transducer and reaches the transducer aftermaking a round trip of length L=2D. The wave travels some whole number nof wavelengths plus a fraction, where wavelength is given by:

$\begin{matrix}{\lambda = \frac{c}{f}} & \left( {{Equation}\mspace{14mu} 16} \right)\end{matrix}$

Where c=sound speed, and f=wave frequency. Using Equation 16, the roundtrip distance to target can be written as:

$\begin{matrix}{D = {\left( {n_{1} + \frac{\phi}{2\pi}} \right) \times \frac{\lambda}{2}}} & \left( {{Equation}\mspace{14mu} 17} \right) \\{\phi_{1} = {{2\pi\; f_{1}T_{1}} = \frac{4\pi\; f_{1}d_{1}}{c}}} & \left( {{Equation}\mspace{14mu} 18} \right) \\{T_{1} = \frac{\phi_{1}}{2\pi\; f_{1}}} & \left( {{Equation}\mspace{14mu} 19} \right) \\{\phi_{2} = {{2\pi\; f_{2}T_{2}} = \frac{4\pi\; f_{2}d_{2}}{c}}} & \left( {{Equation}\mspace{14mu} 20} \right) \\{T_{2} = \frac{\phi_{2}}{2\pi\; f_{2}}} & \left( {{Equation}\mspace{14mu} 21} \right)\end{matrix}$

Where the ϕ/2π term is equivalent to time as per (19) and (21). If n₁=0,(15) is unambiguous and since the frequency f and fluid sound speed areknown a priori D can be determined by direct measurement of the phase ofthe received signal relative to the transmitted signal.

When n₁>1, D is ambiguous as the measured phase values repeat atintervals of 2πf. The value n₁ can be extracted from the measured databased on the idea that the differential phase shift of twosimultaneously propagating waves of differing frequencies will generateprogressively larger phase shifts; the value of the increase is aconstant φ_(d) as the travel time increases. Detecting the two signalsat some distance D and knowing they began traveling at the same time themeasured phase can be divided by φ_(d) to extract the number of completewave periods that occurred to generate the measured phase difference.

Mathematically,

$\begin{matrix}{{{\phi_{1} - \phi_{2}}} = {{D\left( {\frac{1}{\lambda_{1}} - \frac{1}{\lambda_{2}}} \right)} = \frac{\Delta\phi}{2\pi}}} & \left( {{Equation}\mspace{14mu} 22} \right)\end{matrix}$

The phase difference embodiment modifies the time difference embodimentby applying a fixed frequency f₁ to the phase measurement in one of thefluid chambers, and another fixed frequency f₂ to the other fluidchamber. The exact frequency values of f₁ and f₂ are not critical to thefunction of the invention, however it is critical that the frequenciesare selected to ensure that n₁=n₂ or n₁=n₂+1. This relationship ensuresthat the value of φ_(d) remains constant over the entire measurementrange.

Rewriting (15) using (19), (21):

$\begin{matrix}{{\left. {Stroke} \right.\sim\frac{\frac{\phi_{1}}{2\pi\; f_{1}} - \frac{\phi_{2}}{2\pi\; f_{2}}}{\frac{\phi_{1}}{2\pi\; f_{1}} + \frac{\phi_{2}}{2\pi\; f_{2}}}} = {\frac{\phi_{1} - {\frac{f_{1}}{f_{2}}\phi_{2}}}{\phi_{1} + {\frac{f_{1}}{f_{2}}\phi_{2}}}}} & \left( {{Equation}\mspace{14mu} 23} \right)\end{matrix}$

The phase embodiment maintains the same ratiometric benefits ofmechanical length and sound speed insensitivity as the time of flightembodiment. The frequency f₁ is related to f₂ by a fixed ratio. Thiscondition ensures the relative phase difference remains constant withcircuit aging and temperature change. Other embodiments can remove thisrestriction with the result of reduced aging performance and temperaturecompensation without substantively altering the method.

As an extension of the linearized ratio metric position sensors of FIG.1-8, a modification can be made to place the transceiver elements inmore preferential locations. In the examples of FIGS. 9-15, this isachieved by positioning a transceiver element (XDCR1) in reflectivecommunication with an effector, and a second transceiver element (XDCR2)located in a static chamber sharing common fluid (e.g., fuel), andtherefore approximate physical properties with the first transceiverelement (XDCR1). The result of a static reference is a logarithmicdifferential/sum output which will be outlined below. The transceiverelement XDCR1 transmits a signal which reflects off the effector and isreceived by the transceiver. The measured time in conjunction with thesound speed defines the distance to the effector:

$\begin{matrix}{L_{1} = {t_{1} \times C_{1}}} & \left( {{Equation}\mspace{14mu} 24} \right)\end{matrix}$

The transceiver element XDCR2 of the static chamber follows a similarform:

$\begin{matrix}{L_{2} = {t_{2} \times C_{2}}} & \left( {{Equation}\mspace{14mu} 25} \right)\end{matrix}$

The fuel of the second transceiver element XDCR2 in the static chamberis supplied from a shared source as the first transceiver element XDCR1.The transducers and the effector can be configured such that the signalsare used as a ratiometric device, rather:

$\begin{matrix}{\left. {Stroke} \right.\sim\left. \frac{t_{1} - t_{2}}{t_{1} + t_{2}} \right.\sim\frac{\frac{L_{1}}{C_{1}} - \frac{L_{2}}{C_{2}}}{\frac{L_{1}}{C_{1}} + \frac{L_{2}}{C_{2}}}} & \left( {{Equation}\mspace{14mu} 26} \right)\end{matrix}$

Since C₁˜C₂, as a ratio metric device, the effects of sound speedcharacteristics are cancelled out and not required for evaluation ofposition. XDCR1 monitors the dynamical position of an effector whileXDCR2 acts as a constant distance reference. In some configurationsXDCR1 and XDCR2 can be the same transceiver element, with output energydivided between appropriate surfaces. As a result, the output ofequation 26 is logarithmic. A sample logarithmic output is provided inFIG. 19.

All of the embodiments described can provide, in addition to position,direct measurement of actuator velocity and/or actuator acceleration bythe incorporation of signal processing using multiple position samplesand/or by extracting Doppler shift information from the transducer(s)signals. Only one of the plurality of transducers is required to beprocessed, however. Doppler processing of two transducers provideshigher accuracy by a factor of 1.4× over a single channel.

Ultrasonic pulses are emitted periodically as is prescribed for positionmeasurement. Following each emission, the returned echo signal issampled at a fixed delay after the emission. From equations (25) and(26), this delay defines the depth.

As the actuator moves between the successive emissions, the sampledvalues taken at time T_(s) will change over the time. Unfortunately, asthe velocity information is available only periodically, the techniqueis limited by the Nyquist theorem. This means that a maximum velocityexists for each pulse repetition frequency (F_(prf)):

$\begin{matrix}{V_{\;{m\;{ax}}} = \frac{F_{prf}C}{4F_{e}\cos\;\delta}} & \left( {{Equation}\mspace{14mu} 27} \right)\end{matrix}$

The maximum measurable depth is also defined by the pulsed repetitionfrequency:

$\begin{matrix}{P_{m\;{ax}} = \frac{C}{2F_{prf}}} & \left( {{Equation}\mspace{14mu} 28} \right)\end{matrix}$

Therefore the product of P_(max) and V_(max) is constant, and is givenby:

$\begin{matrix}{{P_{{ma}\; x} \times V_{m\;{ax}}} = \frac{C}{8F_{\theta}\cos\;\delta}} & \left( {{Equation}\mspace{14mu} 29} \right)\end{matrix}$

FIG. 16 is a block diagram of an example transducer controller 1600. Theillustrated example outlines a digital solution to achieving timetransits and signal processing. In the sample provided, a digital core1610 (e.g., a DSP) outputs a signal RX burst signal and a TX enablesignal. An RF amplifier 1612 is energized and amplifies the RX burstsignal to appropriate voltages for the respective sensing system. Theamplified signal then passes through a directional coupler 1614 andexcites a pair of transceiver elements 1620 a, 1620 b. In someimplementations, a directional coupler or some other blocking circuitcan be placed in the transmission line to block or limit the echosignals from each transducer from feeding back to the oppositetransducer or to the pulse generator. The desired signals returning froma pair of reflective surfaces 1622 a, 1622 b is passed through thedirection coupler 1614, through a T/R switch 1630 and amplified througha pre-amp 1632 to usable voltage levels prior to receipt at the digitalcore 1610. Within the digital core 1610 digital signal processing iscompleted for determination of time transits and ultimately ratio metricposition of the effector, linear or logarithmic. With the digital core1610 accessible, complex DSP tasks can be performed enabling thedetermination of effector parameters such as velocity, acceleration, andhealth monitoring prognostics.

However, in certain aerospace and other high-temperatureharsh-environment applications, ambient temperatures can exceed thecapabilities of silicon-based semiconductors. In some embodiments,DSP-based correlation processors, memory, ADC/DAC, and other standardcomponents needed to support such a system may not currently exist in aform that can withstand such harsh environmental conditions. Anadvantage of an analog correlator is that it can process signals in realtime and provide a continuous voltage output at low frequency, and canreduce or eliminate the need for an ADC, sampled data processing,memory, and/or discrete arithmetic methods. Analog correlators cantherefore be well suited for high-temperature implementation inwide-bandgap (WBG) semiconductor processes. This opens the potential forimplementation of a complete time-of-flight correlation system using WBGsemiconductors capable of supporting the required level of deviceintegration with existing IC process technologies.

FIG. 17 is a block diagram of another example transducer controller1700. The illustrated example shows an embodiment of a transducercontrolling circuit using an analog approach in the time domain. Thiscircuit excites transducers 1701 a, 1701 b simultaneously and thenmeasures the time difference between return echoes from the twotransducers. The output from the circuit is the difference as a ratiometric voltage proportional to the relative position of the two targets.A detailed description of the functional blocks follows.

A pulse generator 1710 is triggered by a pulse repetition rate (PRR)signal synchronized with the behavior of a time of flight (TOF)difference over sum block 1712 and governed by the TOF physics of themechanical system. The electrical pulse generated is simultaneously sentto both transducers 1701 a, 1701 b over a bifurcated transmission line.A pair of directional couplers 1714 a, 1714 b or some other blockingcircuit is placed in the transmission line to block or limit the echosignals from each transducers 1701 a, 1701 b from feeding back to theopposite transducer or to the pulse generator 1710. The pulse istransformed by each transducer to an ultrasonic incident wave, 11 and 12respectively. The reflected wave from each transducer, R1 and R2respectively is transformed back to small voltage signals.

The remaining description will focus on one path of the signal conditioncircuitry shown in FIG. 17. Both paths behave substantially identically.

A low noise RF amplifier (LNA) 1720 amplifies the weak signal beforepassing it to a band pass filter 1722 which is designed to allow onlythe frequencies of interest to be forwarded to the remaining circuit.

An envelope detector 1724 is an amplitude demodulator configured toextract a baseband envelope pulse from a high frequency AC signal. Theenvelope is then passed through a constant fraction discriminator 1730(CFD) circuit to a timer 1740 to obtain an amplitude invariantzero-crossing time stamp for the return echo signal.

Signals from both paths shall now again be used for the remainder ofthis description.

FIG. 18 is a block diagram 1800 of time-of-flight and ratiometricfunction blocks. The circuit in the illustrated example provides a basisfor a description of the example timer 1740 and TOF difference over sumblocks 1712 of FIG. 17.

A free running oscillator 1810 provides a time-based trigger to both apulse generator 1812 and a reset signal to two ramp generators 1814 a,1814 b. A linear voltage ramp is fed to sample and hold (S-H) function1816 a, 1816 b to start a sampling timer running. When a CFD outputsignal 1820 a from transducer 1 crosses zero, a comparator 1822 a outputactivates the hold on the S-H 1816 a stopping the timer and latching theecho return time t1 as a specific voltage level on its output.Similarly, the echo return time t2 voltage equivalent is processed andlatched on the output of the S-H function 1816 b based on a CFD outputsignal 1820 b from transducer 2 and a comparator 1822 b output.

These voltages (times) are continually updated with each successivepulse-echo cycle at the rate set by the PRR frequency. In so doing, thechange in position of the target is recorded as a continuous sequence oft₁ and t₂ times.

The two voltages values, t₁ and t₂, are then simultaneously fed into adifference amplifier 1830 to get a differential time t₁−t₂, and asumming amplifier 1832 to get t₁+t₂. These difference and sum voltagesare then input to an amplifier 1834 that performs a division and arrivesat the difference over sum ratio-metric output, (t₁−t₂)/(t₁+t₂).

If two opposing transducers are used on either side of the movingtarget, an output 1840 will be a linear relationship of seconds/secondvs position. If one of the two transducers is fixed, the resultingdifference over sum relationship will be a logarithmic (log 10) profileinstead of a linear one. To make subsequent use of this output easier touse, the logarithmic signal can be linearized by an antilog circuit1844. An inverse exponential or anti-log can be realized by the equation10x=e^(2.3x). An exponential amplifier can be accomplished with ananalog circuit. By setting the logarithmic difference over sum voltagefrom the stationary target set-up=x, a three-step process can arrive ata linear ramp on output 1842 substantially equal in range to the naturallinear ramp at output 1840 that occurs for an opposing transducerset-up. First multiply x by 2.3, then pass it through the exponentialamplifier to realize the e^(2.3x) operation. Finally, a linear scalingand offset function, y=mx+b, can fit the linear ramp to the desiredrange. FIG. 19 is a graph of an example log 10 to linear transformation.In some implementations, a notional circuit could be used to performthis function. The log 10 and resulting linear signals are shown in FIG.19.

In yet another embodiment, the ToF sensor can consist of a transmitterand correlation matched-filter receiver along with a voltage tofrequency converter that produces a continuous frequency outputproportional to the measured ToF. The transmitter can be a simple pulsegenerator that periodically charges and dumps an accumulated charge onthe piezo transducer, exciting the crystal step response. A systemfunctional block diagram of an example analog cross-correlation module2000 is shown in FIG. 20.

In this illustrated embodiment, the previously described CFD and ramptimer can be replaced with a frequency domain correlator or matchedfilter in the receiver. A correlation time-of-flight receiver wouldconsist of a correlator 2010, a low-noise amplifier (LNA) 2012, acomparator 2014, a ramp or sawtooth generator 2016, a zero-order samplehold 2018, and a voltage-controlled oscillator. A received signal isamplified by the LNA 2012 and correlated with a local template impulseduring a pulse repetition period (PRP), and its output is sampled andheld to detect whether there is a signal in the PRP observation window.The analog correlator 2010 includes a standard Gilbert cell (GC), loadcapacitor, and other supporting circuits. An example embodiment of suchan analog correlator is presented as FIG. 21.

After a fixed post TX dead-band interval, the standard GC multiplies thereceived signal with the template, and the product is integrated by theload capacitor. To evaluate the performance and describe the operationof the correlator, a two-tone signal model is also described.

The correlator 2010 is used to detect the presence of signals with aknown waveform in a noisy background. The output is nearly zero if onlynoise is present; otherwise, the energy of the received signal isintegrated with the local template waveform over a fixed time intervalto obtain a voltage output above a predefined threshold. Thecross-correlation function can be described by the following equation:

$\begin{matrix}{C_{c} = {{\int_{t0}^{{t0} + T}{\cos\left( {{\omega_{1}t} + \varphi_{1}} \right)}} + {{\cos\left( {{\omega_{2}t} + \varphi_{2}} \right)}dt}}} & \left( {{Equation}\mspace{14mu} 30} \right)\end{matrix}$

Where LO(t) is the local template signal, RF(t) is the input F frequencysignal of the correlator, and T is the integration period.

The correlation process can be divided into two steps. The first stepinvolves multiplication of the received signal and the referencewaveform (local template signal) using a GC. The second step involvesintegration of the output current via a capacitor.

An example of a correlator 2100 is depicted in FIG. 21. A GC multiplier2110, as a current-mode element, outputs a differential current 2120.The typical resistive or inductive load of a standard Gilbert mixer isreplaced by two current sources 2130 a, 2130 b, and a capacitor 2132across the differential output nodes. Because the common-mode part ofthe output current is absorbed by the current source load, thedifferential output current is directly fed into the load capacitor. Asa result, the capacitor integrates the current and outputs a step-likevoltage. A switch 2134 controlled by an internal clock is used todetermine the integration interval and to clear the charge in thecapacitor 2132 at the end of each interval.

Clocking is achieved using a ramp generator and comparators configuredto trigger at voltage set points along the ramp waveform. An example ofsuch a circuit 2200 is shown in FIG. 22. Relative timing between clockevents is maintained ratio metrically using a fixed voltage dividerhaving constant current source bias. A ramp 2202 is generated bycharging a timing capacitor 2204 using a mirror 2212 of a dividercurrent source 2210. In some implementations, use of mirroring can atleast partly cancel relative drift between the voltage set points andthe PRP ramp voltage, minimizing timing drift over circuit element andIC process variation.

The sequence of control gates is shown in FIG. 22. The PRP ramp 2202 isa free-running oscillator. A cycle begins when the timing capacitor 2204is reset and the PRP ramp voltage is zero. As the capacitor 2204charges, the ramp voltage increases, triggering a TX Gate comparator2220 and firing the transducer driver circuit. A dead-band interval isbuilt-in to the timing to disable the receiver during a short blankinginterval. This dead-band prevents reverberations and other false signalreturns from triggering the correlator prematurely. After the dead-banddelay an Xcorr Gate comparator 2222 fires, allowing the integrationswitch on the GC to open and charge the load capacitor. The integratedload capacitor voltage represents the time cross-correlation of thetemplate signal and the receiver signal.

The point in time of the measurement interval at which the correlatoroutput voltage switches is determined by the ToF of the receiver inputsignal. Once the correlator switches the voltage on the load capacitorwill begin to decay as soon as the receive echo passes, which willdegrade accuracy. To prevent this, the PRP ramp and correlator outputare compared by an SH Gate comparator 2224 to generate a SH Gate. The SHGate activates a zero-order (sample) hold that captures the loadcapacitor voltage at the moment the correlator fires. The SH Gate canactivate any time after the correlator is enabled by the Xcorr Gate, butnot before, as the PRP ramp voltage ensures monotonic sequencing of thegates. When the end of the ToF interval is reached the final PRP EndGate is triggered by a PRP End Gate comparator 2226, resetting thetiming capacitor 2204, and starting the cycle all over again.

Referring again to FIG. 20, the output of the sensor uses the voltage tofrequency (VCO) converter 2020 to map the output of the sample-holdoutput voltage to a scaled frequency proportional to time. The VCOscaling can be adjusted to produce a suitable range as needed by aspecific application.

VCO drift with temperature is a common problem that has a deleteriouseffect on accuracy in aerospace and other harsh-environmentapplications. Those familiar with the art will recognize that there areseveral approaches to managing temperature-induced VCO frequency andgain scaling drift, none of which fundamentally alter the operationprinciples of the system described here. One example method involvesusing combinations of components having complementary temperaturecoefficients in ways that cancel overall frequency drift, gain scaling,or both. Another example method employs a pair of VCOs that have close,but not identical gain scaling functions. As the frequencies drift apartwith temperature, the measured gains and the two output frequencies canbe combined as a system of two equations and two unknowns, allowing thedrift to be compensated. Many other methods beyond those described areknown in the art and will not be enumerated further here.

Due to the integration applied to the TOF through correlation, phasenoise is typically not a significant error term of the correlation.Phase noise, when significant in this embodiment, is an artifact of thespecific VCO implementation, not correlation. Presented above aremethods to determine the position of a dynamic effector that eitherproduce or can generate a ratio metric position through linear orlogarithmic methods. In addition to the physical implementation,outlined are digital and analog solutions for determination of the ratiometric output of the device. This output signal can then be used forcommunication with a PID controller and command source. The ratio metricoutput signal can be used as a feedback variable for a PID controllerand for reporting the position of an effector at the higher-level systemcommand source.

FIG. 23 is a schematic of an example template generator circuit 2300. Insome implementations, the template generator circuit 2300 can be used toproduce a matching step response to a transducer by using matching piezomaterial as a resonant element.

FIG. 24 is a graph of examples of signal timings 2400 provided by theexample circuit 2200 of FIG. 22. In general, PRP ramp-based timing canprovide ratiometric delays from a single-timing capacitor and currentsource, while addition of hysteresis on PRP timing capacitor reset canreduce supply and temperature induced time jitter.

FIG. 25 is a block diagram of an example closed loop control system2500. The system 2500 includes a command source 2510, an end effector2520, and an electronic closed loop controller 2530. In someembodiments, the command source 2510 may be an engine controller. Thecommand source 2510 provides a position request to the electroniccontroller 2530, and the electronic controller 2530 is configured tomove the end effector 2520 via an actuation device.

The end effector 2520 includes a linear feedback sensor 2522. Examplesof linear feedback sensors can include the ratio metric ultrasoundposition sensors presented herein, a linear variable differentialtransformer, a linear hall sensor, an optical sensor, or any otherappropriate linear feedback sensor.

Example actuation devices may include but are not limited to directdrive valves, a pumping system, an electro-hydraulic servo valve, asolenoid, a solid-state actuator, a solid-state pump, or any appropriateactuation devices.

End effectors for position monitoring may include but are not limited tometering valves, regulating valves, equal area actuators, dual areaactuators, and any other appropriate translation device.

The higher-level system controller 2530 is in communication with a PIDcontroller (not shown). The PID controller is configured to activate anactuation device and cause the translation of the end effector 2520. Insome implementations, the PID controller can be configured to adjust thecommand to the actuation device based on a comparison of the currentposition and the commanded position.

The electronic controller 2530 receives from the end effector 2520 afeedback signal 2524. The position of the end effector 2520 can then bedetermined by a feedback conditioner 2532 and a feedback controller2534. In some implementations, the conditioner 2532 and the controller2534 may be the digital or analog systems discussed in the descriptionsof FIGS. 16-23.

The determined position is passed to an outer loop feedback module 2536as a position status for health monitoring and outer loop feedback tothe command source 2510. The determined position is also passed to asumming junction 2538 where the current position is compared to thecommanded position defined by the command source 2510 and a signalconditioner 2540. The difference in the request position and currentposition is provided to a controller 2550, such as a PID controller, andactuates an actuator 2552, such as a brushless DC motor, to move theposition of the end effector 2520. The PID controller (not shown)actively adjusts the actuator based on the current position compared tothe commanded position.

Provided in FIG. 25 is an example configuration of a control system. Theratio metric position sensing solutions and respective circuitry ofFIGS. 1-24 may be in any number of control systems. The ratio metricsensors and digital or analog controller can be applied to many systemsolutions, including others not specifically described in this document.

FIG. 26 is a flow diagram of another example process 2600 for ultrasonicposition sensing. In some implementations, the process 2600 may beperformed by all or parts of the systems and circuits discussed in thedescriptions of FIGS. 9-25.

At 2610 a first emitted acoustic waveform is emitted through a fluidhaving a first acoustic impedance toward a first acoustic interface. Forexample, the example acoustic transceiver 940 a of FIG. 9 can emit theemitted acoustic waveform 942 a toward the face 922.

At 2620, a second emitted acoustic waveform is emitted through the fluidtoward a second acoustic interface. For example, the acoustictransceiver 940 b can emit the emitted acoustic waveform 942 b towardthe face 932

At 2630, the first acoustic interface reflects a first reflectedacoustic waveform based on the first emitted acoustic waveform. Forexample, the face 922 can reflect the emitted acoustic waveform 942 a asthe reflected acoustic waveform 944 a.

At 2640, the second acoustic interface reflects a second reflectedacoustic waveform based on the second emitted acoustic waveform. Forexample, the face 932 can reflect the emitted acoustic waveform 942 b asthe reflected acoustic waveform 944 b.

At 2650, a first position of the second acoustic interface is determinedbased on the first reflected acoustic waveform and the second reflectedacoustic waveform. For example, the example signal processor 960 canprocess signals from the acoustic transceiver 940 a and the acoustictransceiver 940 b to determine the position of the moveable body 938within the cavity 930.

In some implementations, a first time of flight can be determined basedon the first emitted acoustic waveform and the first reflected acousticwaveform, and determining a second time of flight based on the secondemitted acoustic waveform and the second reflected acoustic waveform,wherein determining a first position of the acoustic interface isfurther based on the first time of flight and the second time of flight.For example, the signal processor 960 can be configured to performprocessing based on the example equations 15-30 above.

In some implementations, the process 2600 can include determining thefirst position of the acoustic interface based on the first time offlight (t₁) and the second time of flight (t₂) can be given by anequation: (t₁−t₂)/(t₁+t₂) (e.g., equation 15).

In some implementations, the process 2600 can also include determining asecond position of the second acoustic interface, and determining aspeed of the second acoustic interface based on the first position andthe second position. For example, two successive position measurementsof the example moveable body 938 to determine a speed of the moveablebody 938.

In some implementations, the process 2600 can include determining areflected acoustic frequency based on one or both of the first reflectedacoustic waveform and the second reflected acoustic waveform, anddetermining a speed of the second acoustic interface based on thedetermined reflected acoustic frequency and a predetermined emittedacoustic frequency of the second emitted acoustic waveform. For example,the signal processor 960 can include a phase detector (e.g., todetermine phase and/or Doppler shifts in reflected signals).

In some implementations, the first acoustic interface can be defined bya face of a fluid cavity having a second acoustic impedance that isdifferent than the first acoustic impedance, the second acousticinterface can be defined by a second face of a moveable body within afluid effector and having a third acoustic impedance that is differentthan the first acoustic impedance, the first emitted acoustic waveformcan be emitted toward the first face through the fluid, the secondemitted acoustic waveform can be emitted toward the second through thefluid, the first reflected acoustic waveform can be based on a firstreflection of the first emitted acoustic waveform by the first face, andthe second reflected acoustic waveform can be based on a secondreflection of the second emitted acoustic waveform by the second face.For example, the sensor housing and the moveable body 938 can be made ofmaterials that have acoustic impedances that are different from theacoustic impedance of the fluid in the cavities 920 and 930. Themismatches in acoustic impedances can cause reflections of the emittedacoustic signals 942 a and 942 b off the faces 922 and 932.

In some implementations, the process 2600 can include determining aphase difference between a second emitted phase of the second emittedacoustic waveform and a second reflected phase of the second reflectedacoustic waveform, wherein determining a first position of the acousticinterface can be further based on the determined phase difference. Forexample, distance can be determined based on example equation 23.

In some implementations, the first emitted waveform can be emittedthrough a first fluid cavity toward a face of the first fluid cavitydefining the first acoustic interface, and the second emitted waveformcan be emitted through a second fluid cavity toward a second face of amoveable member defining the second acoustic interface. For example, theexample emitted acoustic waveform 942 a can be emitted through thecavity 920, and the example emitted acoustic waveform 942 b can beemitted through the cavity 930.

In some implementations, the first emitted waveform can be emittedthrough a first portion of a fluid cavity toward a face of the fluidcavity defining the first acoustic interface, and the second emittedwaveform can be emitted through a second portion of the fluid cavitytoward a second face of a moveable member defining the second acousticinterface. For example, the example emitted acoustic signal 1150 of FIG.11 can be emitted toward the face portion 1130 and the face portion1112.

In some implementations, the process 2600 can include emitting a thirdemitted acoustic waveform through the fluid toward a third acousticinterface, reflecting, by the third acoustic interface, a thirdreflected acoustic waveform based on the third emitted acousticwaveform, and determining a second position of the third acousticinterface based on the first reflected acoustic waveform and the thirdreflected acoustic waveform. For example, in the example system 1500, afirst acoustic signal can be emitted by one of the acoustic transceivers1506 toward the face 1507, a second acoustic signal can be emitted byone of the acoustic transceivers 1518 toward a corresponding face 1517,and a third acoustic signal can be emitted by another one of theacoustic transceivers 1518 toward another corresponding one of the faces1517.

FIG. 27 is a schematic diagram of an example of a generic computersystem 2700. The system 2700 can be a data processing apparatus (e.g.,processor system) used for the operations described in association withthe process 800 according to one implementation. For example, the system2700 may be included in either or all of the signal processors 150, 960,1060, 1560, or the controllers 160, 970, 1070, or 1570.

The system 2700 includes a processor 2710, a memory 2720, a storagedevice 2730, and an input/output device 2740. Each of the components2710, 2720, 2730, and 2740 are interconnected using a system bus 2750.The processor 2710 is capable of processing instructions for executionwithin the system 2700. In one implementation, the processor 2710 is asingle-threaded processor. In another implementation, the processor 2710is a multi-threaded processor. The processor 2710 is capable ofprocessing instructions stored in the memory 2720 or on the storagedevice 2730 to display graphical information for a user interface on theinput/output device 2740.

The memory 2720 stores information within the system 2700. In oneimplementation, the memory 2720 is a computer-readable medium. In oneimplementation, the memory 2720 is a volatile memory unit. In anotherimplementation, the memory 2720 is a non-volatile memory unit.

The storage device 2730 is capable of providing mass storage for thesystem 2700. In one implementation, the storage device 2730 is acomputer-readable medium. In various different implementations, thestorage device 2730 may be a floppy disk device, a hard disk device, anoptical disk device, or a tape device.

The input/output device 2740 provides input/output operations for thesystem 2700. In one implementation, the input/output device 2740includes a keyboard and/or pointing device. In another implementation,the input/output device 2740 includes a display unit for displayinggraphical user interfaces. In another implementation, input/outputdevice 2740 includes a serial link, (e.g., Ethernet, CAN, RS232, RS485,optical fiber), for example, to interface to a remote host and/or tosend measurement results, either in a command/response protocol, or atsome periodic update rate after a short initialization period (e.g., <1sec). In another implementation the input/output device 2740 includes adata bus connection to a second computer system or processor.

The features described can be implemented in digital electroniccircuitry, or in computer hardware, firmware, software, or incombinations of them. The apparatus can be implemented in a computerprogram product tangibly embodied in an information carrier, e.g., in amachine-readable storage device for execution by a programmableprocessor; and method steps can be performed by a programmable processorexecuting a program of instructions to perform functions of thedescribed implementations by operating on input data and generatingoutput. The described features can be implemented advantageously in oneor more computer programs that are executable on a programmable systemincluding at least one programmable processor coupled to receive dataand instructions from, and to transmit data and instructions to, a datastorage system, at least one input device, and at least one outputdevice. A computer program is a set of instructions that can be used,directly or indirectly, in a computer to perform a certain activity orbring about a certain result. A computer program can be written in anyform of programming language, including compiled or interpretedlanguages, and it can be deployed in any form, including as astand-alone program or as a module, component, subroutine, or other unitsuitable for use in a computing environment.

Suitable processors for the execution of a program of instructionsinclude, by way of example, both general and special purposemicroprocessors, and the sole processor or one of multiple processors ofany kind of computer. Generally, a processor will receive instructionsand data from a read-only memory or a random access memory or both. Theessential elements of a computer are a processor for executinginstructions and one or more memories for storing instructions and data.Generally, a computer will also include, or be operatively coupled tocommunicate with, one or more mass storage devices for storing datafiles; such devices include magnetic disks, such as internal hard disksand removable disks; magneto-optical disks; and optical disks. Storagedevices suitable for tangibly embodying computer program instructionsand data include all forms of non-volatile memory, including by way ofexample semiconductor memory devices, such as EPROM, EEPROM, and flashmemory devices; magnetic disks such as internal hard disks and removabledisks; magneto-optical disks; and CD-ROM and DVD-ROM disks. Theprocessor and the memory can be supplemented by, or incorporated in,ASICs (application-specific integrated circuits).

To provide for interaction with a user, the features can be implementedon a computer having a display device such as a CRT (cathode ray tube)or LCD (liquid crystal display) monitor for displaying information tothe user and a keyboard and a pointing device such as a mouse or atrackball by which the user can provide input to the computer.

The features can be implemented in a computer system that includes aback-end component, such as a data server, or that includes a middlewarecomponent, such as an application server or an Internet server, or thatincludes a front-end component, such as a client computer having agraphical user interface or an Internet browser, or any combination ofthem. The components of the system can be connected by any form ormedium of digital data communication such as a communication network.Examples of communication networks include, e.g., a LAN, a WAN, and thecomputers and networks forming the Internet.

The computer system can include clients and servers. A client and serverare generally remote from each other and typically interact through anetwork, such as the described one. The relationship of client andserver arises by virtue of computer programs running on the respectivecomputers and having a client-server relationship to each other.

Although a few implementations have been described in detail above,other modifications are possible. For example, the logic flows depictedin the figures do not require the particular order shown, or sequentialorder, to achieve desirable results. In addition, other steps may beprovided, or steps may be eliminated, from the described flows, andother components may be added to, or removed from, the describedsystems. Accordingly, other implementations are within the scope of thefollowing claims.

What is claimed is:
 1. A position sensor system, comprising: a sensorhousing defining a first cavity having a first face; a fluid effectorcomprising: an actuator housing having an inner surface defining asecond cavity; and a moveable body having a second face and configuredfor reciprocal movement within the second cavity; an acoustictransmitter system configured to emit a first emitted acoustic waveformtoward the first face, and emit a second emitted acoustic waveformtoward the second face; and an acoustic receiver system configured todetect a first reflected acoustic waveform based on a first reflectionof the first emitted acoustic waveform based on the first face, anddetect a second reflected acoustic waveform based on a second reflectionof the second emitted acoustic waveform based on the second face.
 2. Theposition sensor system of claim 1, further comprising a timer configuredto determine a first time of flight of the first emitted acousticwaveform and the first reflected acoustic waveform, and determine asecond time of flight of the second emitted acoustic waveform and thesecond reflected acoustic waveform.
 3. The position sensor system ofclaim 2, further comprising a processor system configured to determine aposition of the moveable body within the second cavity based on thefirst time of flight and the second time of flight.
 4. The positionsensor system of claim 1, wherein the acoustic transmitter system isconfigured to emit one or both of the first emitted acoustic waveformand the second emitted acoustic waveform through a fluid in one or bothof the first cavity and the second cavity, and the acoustic receiversystem is configured to receive one or both of the first reflectedacoustic waveform and the second reflected acoustic waveform from thefluid in one or both of the first cavity and the second cavity.
 5. Theposition sensor system of claim 1, wherein the acoustic transmittersystem is configured to transmit the second emitted acoustic waveform ata predetermined emitted frequency, and the acoustic receiver system isconfigured to determine a reflected frequency of the second reflectedacoustic waveform.
 6. The position sensor system of claim 5, furthercomprising a processor system configured to determine a speed of themoveable body based on the predetermined emitted frequency and thereflected frequency.
 7. The position sensor system of claim 1, wherein:the fluid effector is a linear piston effector; the first cavity is afirst tubular cavity having a first longitudinal end and a secondlongitudinal end defining the first face opposite the first longitudinalend; the second cavity is a second tubular cavity having a thirdlongitudinal end and a fourth longitudinal end opposite the thirdlongitudinal end; the moveable body is a piston head configured forlongitudinal movement within the second tubular cavity; the acoustictransmitter system comprises a first acoustic transmitter arranged atthe first longitudinal end and a second acoustic transmitter arranged atthe third longitudinal end; and the acoustic receiver system comprises afirst acoustic receiver arranged at the first longitudinal end and asecond acoustic receiver arranged at the third longitudinal end.
 8. Theposition sensor system of claim 1, further comprising a unified cavitycomprising the first cavity and the second cavity.
 9. The positionsensor system of claim 8, wherein the first face is at least partlydefined by a shoulder extending between first cavity and the secondcavity.
 10. The position sensor system of claim 1, wherein the acoustictransmitter system comprises: a first acoustic emitter configured toemit the first emitted acoustic waveform toward the first face; and asecond acoustic emitter configured to emit the second emitted acousticwaveform toward the second face.
 11. The position sensor system of claim10, wherein the second acoustic emitter at least partly concentricallysurrounds the first acoustic emitter.
 12. The position sensor system ofclaim 1, further comprising a phase detector configured to determine adifference between at least one of (1) a first emitted phase of thefirst emitted acoustic waveform and a first reflected phase of the firstreflected acoustic waveform, and (2) a second emitted phase of thesecond emitted acoustic waveform and a second reflected phase of thesecond reflected acoustic waveform.
 13. The position sensor system ofclaim 1, further comprising another moveable body having a third faceand configured for reciprocal movement within a third cavity, whereinthe acoustic transmitter system is configured to emit a third emittedacoustic waveform toward the third face, and the acoustic receiversystem is configured to detect a third reflected acoustic waveform basedon a third reflection of the third emitted acoustic waveform based onthe third face.
 14. A method of position sensing comprising: emitting afirst emitted acoustic waveform through a fluid having a first acousticimpedance toward a first acoustic interface; emitting a second emittedacoustic waveform through the fluid toward a second acoustic interface;reflecting, by the first acoustic interface, a first reflected acousticwaveform based on the first emitted acoustic waveform; reflecting, bythe second acoustic interface, a second reflected acoustic waveformbased on the second emitted acoustic waveform; and determining a firstposition of the second acoustic interface based on the first reflectedacoustic waveform and the second reflected acoustic waveform.
 15. Themethod of claim 14, further comprising: determining a first time offlight based on the first emitted acoustic waveform and the firstreflected acoustic waveform; and determining a second time of flightbased on the second emitted acoustic waveform and the second reflectedacoustic waveform; wherein determining a first position of the secondacoustic interface is further based on the first time of flight and thesecond time of flight.
 16. The method of claim 15, wherein determiningthe first position of the second acoustic interface based on the firsttime of flight (t₁) and the second time of flight (t₂) is given by anequation: (t₁−t₂)/(t₁+t₂).
 17. The method of claim 14, furthercomprising: determining a second position of the second acousticinterface; and determining a speed of the second acoustic interfacebased on the first position and the second position.
 18. The method ofclaim 14, further comprising: determining a reflected acoustic frequencybased on one or both of the first reflected acoustic waveform and thesecond reflected acoustic waveform; and determining a speed of thesecond acoustic interface based on the determined reflected acousticfrequency and a predetermined emitted acoustic frequency of the secondemitted acoustic waveform.
 19. The method of claim 14, wherein: thefirst acoustic interface is defined by a first face of a fluid cavityhaving a second acoustic impedance that is different than the firstacoustic impedance; the second acoustic interface is defined by a secondface of a moveable body within a fluid effector and having a thirdacoustic impedance that is different than the first acoustic impedance;the first emitted acoustic waveform is emitted toward the first facethrough the fluid; the second emitted acoustic waveform is emittedtoward the second face through the fluid; the first reflected acousticwaveform is based on a first reflection of the first emitted acousticwaveform by the first face; and the second reflected acoustic waveformis based on a second reflection of the second emitted acoustic waveformby the second face.
 20. The method of claim 14, further comprisingdetermining a phase difference between a second emitted phase of thesecond emitted acoustic waveform and a second reflected phase of thesecond reflected acoustic waveform, wherein determining a first positionof the second acoustic interface is further based on the determinedphase difference.
 21. The method of claim 14, wherein the first emittedacoustic waveform is emitted through a first fluid cavity toward a faceof the first fluid cavity defining the first acoustic interface, and thesecond emitted acoustic waveform is emitted through a second fluidcavity toward a second face of a moveable member defining the secondacoustic interface.
 22. The method of claim 14, wherein the firstemitted acoustic waveform is emitted through a first portion of a fluidcavity toward a face of the fluid cavity defining the first acousticinterface, and the second emitted acoustic waveform is emitted through asecond portion of the fluid cavity toward a second face of a moveablemember defining the second acoustic interface.
 23. The method of claim14, further comprising: emitting a third emitted acoustic waveformthrough the fluid toward a third acoustic interface; reflecting, by thethird acoustic interface, a third reflected acoustic waveform based onthe third emitted acoustic waveform; and determining a second positionof the third acoustic interface based on the first reflected acousticwaveform and the third reflected acoustic waveform.
 24. A non-transitorycomputer storage medium encoded with a computer program, the computerprogram comprising instructions that when executed by data processingapparatus cause the data processing apparatus to perform operationscomprising: emitting a first emitted acoustic waveform through a fluidhaving a first acoustic impedance toward a first acoustic interface;emitting a second emitted acoustic waveform through the fluid toward asecond acoustic interface; reflecting, by the first acoustic interface,a first reflected acoustic waveform based on the first emitted acousticwaveform; reflecting, by the second acoustic interface, a secondreflected acoustic waveform based on the second emitted acousticwaveform; and determining a first position of the second acousticinterface based on the first reflected acoustic waveform and the secondreflected acoustic waveform.